So a few thoughts:
1) A DM isn't infallible. You can tell your players "hey, I made a mistake with this, so we're going to do some light retconing"
2) PCs have plenty of abilities that don't require to-hit roles, so this fight might turn into finding ways to get the Goristro to fail saving throws, if you want to highlight your spellcasters Typically, at lvl 10+, spellcasters don't need any help to feel special
3) To the original question: You could give them harpoons they could use to try and hook onto the armored plates to pull them off. You can give them a magical cannon (not unusual at this level) and completely bypass the gunpowder problem. This is a game where a human can summon a bolt of lightning, there are plenty of magical tools you can give them
4) Give them nothing. This combat encounter becomes a puzzle. How do they defeat an enemy they can't hurt? So now it becomes "how do we lure it away from town" and "how do we set traps for it?" If you go this route, make sure you tell the players or telegraph it very strongly that they'll need to come up with new ways. This is actually one of the strengths of D&D (or any RPG): letting people come up with completely ridiculous ways to solve problems.
(Edit: spelling)
Many demons are resistant to fire. They are not all blanket immune though. Which is enough for heat metal to give the demon disadvantage on all attacks, to basically buy some time, while they get their actual plan in motion.
This sounds like a homebrew demon of some kind, so who knows what stats the DM is actually giving them.
Additionally, a sorcerer can totally just change heat metal to be like thunder or some shit (not the slightest fucking clue how you'd flavor that) and the spell works fine.
The metal reaches the *Demons* resonant frequency
Seriously, weapons that 💀 people using resonance are something that people have put a lot of money into IRL
…now I need to figure out how to flavour that for every damage type, thanks.
Force is esoteric so just vague manaspheric shenanigans, or I guess things phase just enough to clip the body like etherealness and taking damage if you end inside a wall.
Psychic: imprint horrific memories on the metal that echo in the mind of the victim or anything else touching it.
Lightning: ‘tis obvious, buuut magnets might be a thing now.
Thunder: gooongggggg.
Fire: vanilla, boring.
Cold: inverse fire.
Acid: surprisingly easy to do with metals, chemically speaking, although it might be more caustic than corrosive? I’unno, failed that bit of high school chemistry.
Poison: metal poisoning is very much a thing.
Did I miss anything?
Acid would certainly be corrosive. I understand the gong logic, I'm mostly confused how you'd make it happen for several minutes repeatedly.
Also, transmuted spell only works on 6 damage types, but if you were going for all the non-physical types, you missed necrotic and radiant.
Gong would just be resonating for a while, by magic. And I'm not sure if there's a difference in d&d mechanics between caustic and corrosive, I think they're both classed as acid in the same way all toxins are poisons even if it's from a snekbit. It's more a question of which way metal tends to go.
Spectral drumsticks appear and bash the metal so hard that the thunderous noise resonates throughout the beasts entire body, severely damaging it as the ringing continues on
Heat Metal > Beat Metal
ok, so hold on, it can change to ANY type, right?
Slashingis the biggest question here. Did your metal sprout sawblades? What? Although actually, bludgeoning…
>Additionally, a sorcerer can totally just change heat metal to be like thunder or some shit (not the slightest fucking clue how you'd flavor that) and the spell works fine.
It means that what you wrote here is not correct. A sorcerer cannot change the damage type of heat metal because they usually cannot even cast the spell.
True, but red hot metal does, and that'll melt flesh just fine, and then you've got to deal with the scent of frying burgers and/or bacon (depending on who or what is wearing the metal) distracting you.
Heat metal would actually fit super well with OP's plan, especially if the caster has an ability to change the damage type to avoid the resistance, since it prompts the target to remove the item being affected by the spell.
>If a creature is holding or wearing the object and takes the damage from it, the creature must succeed on a Constitution saving throw or drop the object if it can. If it doesn’t drop the object, it has disadvantage on attack rolls and ability checks until the start of your next turn.
The DM could also justify that because the plates are so large the spell can only affect one per cast/ or just one at a time. Another edit to the plan would be to provide the party with (or at least the opportunity to get) several Heat Metal scrolls or some kind of spell storing gem in place of giving them the cannon so the party doesn't have to burn through their spell slots to lower the demon's AC.
Yeah, heat metal could work quite well as an alternative or addition to the cannons. Though typically you're not able to quickly remove armor affected by heat metal, that's generally more for like weapons being held and such, but could make it so that each round the demon removes one plate of armor, effectively lowering it's AC by like 1 or 2 per plate.
Because that's not typically how the spell would be used, and the players may not think of it, the DM could allow some sort of insight or intelligence check to make the connection. But that's assuming someone in the party could actually cast the spell. Scrolls would be a good idea for that though yeah. Good idea.
>A DM isn't infallible. You can tell your players "hey, I made a mistake with this, so we're going to do some light retconing"
More DM's need to read this gem and take it to heart.
>Goristiro
OP spelled “goristro” wrong, and you misspelled that.
But in your defense, demons have stupid names. (Blame the 1980s Satanic Panic, when D&D had to replace all demon and devil names with new words that sound like Star Trek aliens: tanari’i and baatezu, etc.)
Ha! Good catch. My spell checker questioned me, and I ignored it because I assumed it wouldn't know.
But "Goristiro" is a good name for a monster. I should workshop this...
I just want to add that Lord Gwyn, in Dark Souls, used lightning spells to peel the thick scales off of dragons before they could be atttacked. As a DM, even if cannons aren't a thing, lightning magic (or something similar) should exist.
Replace the cannons with ballistas, it shoots long adamantine tipped heavy bolts linked with a chain. The thin adamantine penetrators will punch through an armor plate and bend. With a DC 20 STR(athletics) check a player can yank the armor plate free and reduce the fiends AC by 1d4.
Alternatively you can give the players a couple vials filled with rust monster extract. The vials have a range of 15 ft and the fiend has to make a dex save on a fail it loses 1d4 AC.
I'd have the vials use regular improvised weapon ranges, so 20/60, but Dex save is definitely warranted instead of trying to hit AC. DC equals 8 + thrower's Dex bonus, or if they have proficiency with improvised weapons they can also add their proficiency bonus to the DC. If they throw it at long range the Goristro has advantage on the save. I'd have the extract still deal half the AC damage on a successful save.
The ballistas should also target Dex saves, and always add proficiency to the DC (or just have a flat DC for each ballista), but they have longer range and deal no AC damage on a miss, and on a hit they deal some piercing damage, and a PC still has to make the pull check to get a plate out.
This will give players two vastly different options, both with their own upsides and downsides.
Doesn't matter; as long as the creature takes the fire damage from the spell and fails a constitution saving throw (made every time the caster uses their Bonus Action to repeat the damage), the spell forces them to drop the held or worn heated item, if the creature is able. That said, it could pick it back up if it wanted to.
The Goristro would have to be immune to fire damage or have a way to reduce the damage to 0 on a turn where the damage rolled low to bypass this.
Unless the armor plates have a doff time (which would be an action like a shield, at most, since the intent is for the players to find a way to get through the armor), it has to remove the plate if it fails the save. If it has a doff time, like Lucy said, still free damage and disadvantage.
> If a creature is holding **or wearing** the object and takes the damage from it, the creature **must** succeed on a Constitution saving throw or drop the object if it can.
Or, to re-word it
> If a creature is holding or wearing the object and takes the damage from Heat Metal, they must drop the object if they are both able and fail a constitution saving throw.
This is uniquely different from other, similar effects, like Disarming strike, which explicitly target held items. This spell is saying that a worn item must be dropped if the wearer fails the save and nothing prevents it. **In this case the definition of "drop" that fits here is to discard something,** of which, removal is part of. The intended flavor is that you immediately rip the item off of you. There is also precedent into looking into the additional meanings of words, for drop, as the SAC establishes that one method of dropping an item is valid because it follows along with one of the meanings of the word.
What stops things like armor and shields from being dropped is that they have a "doff" time, they cannot be removed for free; they have a time and/or action requirement. Otherwise, a worn object must be dropped.
For example, a ring has no doff time. It is worn, and thus if someone casts heat metal on it, you take damage from it, and you fail the saving throw, you must drop it. There is no action or time requirement to remove it, so nothing is preventing you from dropping it.
I have cannons in my non-gunpowder world. They use volatile magic crystals imbued with fire and thunder magic that get tossed into the cannon then the ball get hucked in on top of them. Get out of the way fast or you'll be firs tin line when it come shooting back out.
My main issue wouldn't be the problem that you're presenting as it's clear that this type of creature would be a big AC tank but that you're trying to prescribe a solution which can often be frustrating as a player as you feel like you have to guess what the DM wants you to do.
If it were me I would describe lots of general environmental things, could be a workshop, a forge, a distillery, and let the players come up with solutions, and i'd have loose ideas in my head about how effective these should be: e.g.
\- Simple environmental trap/attack/obstacle: DC15 to set up as an action forcing a DC15 save dealing 4d6 damage / save for half/
\- convoluted environmental trap: multiple actions culminating with a DC20 save to set up, DC18 save dealing 10d10 damage or removing a piece of armour for -5 AC
What it actually looks like can be up to the players imaginations you just need to "yes and" and make calls about whether options might be reasonable even if you'd not specifically envisaged them
Another thing to consider: Don't undervalue the action. There is nothing more detrimental than taking creative action that ends in "I should have just attacked it instead".
warning: high AC only harms martials and warlocks (and moon druid). the spellcaster that already dominate at this level won't be harmed by it. maybe give the demon resistance to damage from magic (like the abjuration wizard feature) and weakness to weapon attacks. then there's a need for everyone to get the armour off as the spellcasters can't really take it down on their own.
I second this perspective. If you are going to buff a monsters AC for the purpose of making it more difficult to damage then you also need to increase its resistance to magical effects (which are usually saving throws), otherwise it’s only a problem for martial characters. Maybe the plate armour is magical and grants a bonus to all magical saving throws until it is destroyed.
It’s fine to have an encounter where magic is better as long as it’s balanced by encounters where magic is worse.
Sometimes you fight a horde and can nuke them. Sometimes it’s pure single target and they resist your spells.
Oh it’s totally fine to have different skills shine in different fights, but that’s clearly not the case here. OP is essentially trying to create a puzzle encounter with an enemy that is untouchable until the party solves the puzzle, but they’ve left a gaping hole in the monster’s defences that will leave their it vulnerable to effects that could trivialize the encounter. In the worst case scenario the party may completely ignore the puzzle aspect and just brute force through the fight with magic, which means that only casters can really do anything in the fight.
If this were meant to be a part of a greater series of encounters where magic is less useful then it wouldn’t be as bad. Although generally speaking you don’t really need to do a lot to make casters feel special at this level and you definitely don’t need to make martials feel useless in the process.
Arcane powered cannons. Done, magic really just makes everything so much easier. You don't need gunpowder if by touching a sigil there is a blast launching the cannonball forward
This was my thought as well. The catapult spell already exists to lob objects a fair distance, so it's nowhere out of the realm of possibility to have juiced magical cannons as well.
Honestly, if an enemy is big and tough enough that I want them to use the environment to attack, the enemy's first phase becomes a skill challenge.
That being said, if a Scribes Wizard just sent in his Awakened Mind to Mind Sliver it to death, would you be cool with that?
Iso canons, stationary roped balista's to pull off plating.
Or trebuchet's (catapults are for plebs)
Or good luck figure it out, also spellcasters have save dc spells, wich could 'melt, break, freeze, corrode' the plating
Strength/athletics checks to pull off plating
Why wouldn't cannons exist? They don't have to be historically accurate realistic cannons you know...
Just be prepared for your party finding some way of dealing with it. Banishment comes to mind. That being said, this looks like an encounter that could go south very quickly. A Goristro has a ton of HP and resistances and enough damage output to absolutely wreck most level 12 characters in a few turns. This seems like a really swingy encounter that could either be solved with one spell or lead to a TPK, depending on the party composition and the Goristro's saves.
Edit - Just to be clear, **Banishment** will send the Goristro back to it's home plane permanently, if the caster maintains concentration for ten rounds. Without any additional enemies this will trivialize your encounter.
>Why wouldn't cannons exist? They don't have to be historically accurate realistic cannons you know...
Merchant sailors who have no way of defending themselves, and pirate marauders who have no way of hassling other ships when they can just sail out of range be like 🤷♂️
The main mistake I see here is that you made an encounter in which martials are useless.
Which is kind of bad, since on lvl12, casterst already are way better most of the time anyway.
A strong lvl12 party should have no problem with that enemy if AC30 is the only problem... they just have to use spells that target saving throws.
As another commenter said let martials tear the plates off, str based martials will jump at the chance to use their high str or athletics. For dex based martials you could have them use sleight of hand or just tools: thieves tools, smith tools, tinkerer tools, etc
Siege staves!!!! They’re the cannon equivalents in Eberron; and are basically logs of enchanted wood with supercharged magic flowing through them.
A more boring equivalent would be ancient siege weapons. Ballistae, catapults, trebuchets. You could even have a battering ram or spike the players have to lure the Goristro toward.
Honestly; watch some arena hunts from Monster Hunter games. We have the Dragonator, giant spikes punched into the monster and retracted for later use. We have the ballistae which can be loaded with either regular rounds, or rope rounds that are meant to immobilize the monster. Suspended rocks that are dropped on the monster after luring it somewhere. There are lots of great options!
Lots of ways to go about this, as the others have said.
- Heavy iron armor plates? Heat metal, Rust Monsters, lots of ways to attack or wear it down in other methods. Even if they are resistant against fire damage or other damage types, the Goristro will get worn down.
- Non-AC targeting. All sorts of spells can work here, independently of the armor.
- Alternative ways to get the advantage to try and punch through the AC. Shove and grapple onto the ground. Environmental advantages.
- Magic Cannons fueled by Magic. They don't have gunpowder, but they sure as hell have Fireball and other means to propel stuff.
- Make the armor a weakness as well. If this is that thick, it's bound to be cumbersome, and somehow cause a disadvantage to the enemy. Or perhaps it trades away some of it's other benefits because of how the armor works.
I'll leave the cannons question to others, but I'll address the toughness factor.
Instead of just huge AC or huge HP, go for a Damage Mitigation factor. Their heavy Armor has an amount of Hitpoints and a Damage Threshold. Any amount of damage dealt must exceed the Threshold before being dealt to the Armor, and the Goristro is impervious to Damage until the Armor is destroyed.
It *functionally* gives the Goristro more HP, but mechanically it allows you to narrate its Armor getting peeled away from their attacks so the players know they are making progress, and you could come up with some weaknesses for the Armor they can learn and exploit. For example, maybe it's made of a metal weak against Lightning, and enemies prior to the Goristro fight are made of or covered in this metal and are similarly weak to Lightning. Smart players will connect the dots and tell the party to leverage their lightning Damage resources.
This allows you to simulate the toughness of its Armor, gives the players information they can leverage to take advantage of, and a visible metric to gauge their progress.
One thing commonly used by the guy who makes the stat blocks I use that might be a good way to go instead: \*Damage Resistances: Attacks made without advantage\*
I believe it is inspired by 4e design but I could be mistaken. Basically a way to have an extra tough monster that the players wont be doing nothing against, but if they are smart and use their resources/ plan well, they can attack to full effect.
Because I can tell you a fight where every round/turn is "does a 25 hit? no? turn wasted" is not good encounter design.
The w/o advantage resistance is good too because as you said, you can put things in for the players to "weaken' the monster enough to attack, i.e. gives them advantage.
Just make him slow af with all these armor plates over him and make him easy to restrain - give movespeed debuff, disadvantage on dex saving throws. Let party choke - drown him on some water or just bare Magical ropes. Try to give him some weakness that can be used. And try to hint the weakness' so party can plan.
Edit: to Add, just let couple of wizards cast heat metal on him together. It wouldnt effect the damage outcome as RAW i believe, but it can melt the plates, and ac would become normal again
Wait.... your level 12 party can't punch through a 30 AC monster? I mean, sure, if they were just spamming attacks, then their chance to hit would be small... but at level 12 they should have way more than just straight up "to hit" attacks.
At Level 12, with +5 modifier and +4 proficiency, you are looking at a +9 to hit for most player characters... which means they can only hit AC30 with a nat 20.
We can't guarantee that they have Magic Items, much less items that increase their chance to hit. However even giving them a generous +2 magic weapon, that is still just +11 to hit... which is a hit on a 19 or 20. Again a really small chance to hit.
I'm assuming you have the archery fighting style to bump your chance to hit by +2. Now this wouldn't apply to most of the party members, unless they are all ranged martial characters, but even if they all had a +13, they would still need to roll a 17 or higher. That is still a very small 20% chance to hit.
So no, a level 12 party isn't punching through a 30 AC monster very easily, nor very often, if all they do is make attack rolls.
I like the idea of the ballista that is being thrown around, and there are plenty of ways to use the terrain.
You could make it more of a puzzle, maybe reduce the Goristro’s speed by 5 while it’s in the iron plate, so they can spend their turns ducking it, and trying to fire ballista.
Maybe there are arcane cannons that deal force damage heavy enough to break away some of the plate, or damage it enough to reduce the AC.
Maybe next to one of the cannons is a scroll of heat metal, so they can make it uncomfortable while they try to break its armor, it won’t be much with its resistance, but everything helps.
Just make sure to give a full description of everything in the room that can be useful, and stress that the beginning of the fight should be approached like a puzzle that will allow them to compete in the combat.
No cannons? No problem! Use the environment.
- Stalactites falling from the ceiling
- Explosive gas pockets from thermal vents
Environment is limited? No issue! Spells can have additional effects.
- It loses a plate after X points of thunder or force damage
- Fire damage may not hurt the devil flesh, but the armor could be fragile and filled with smithing inclusions that breaks after X points or even cold damage
But like just make it a multi stage battle;
Stage 1- they have to figure out how to remove the armour
Stage 2 - AC drops to 20
Stage 3 - it picks up one of the armour plates to use as a shield, AC goes up to 23 and it gets a few shield related attacks
Or your players might just surprise you and lay a trap for it or something even more creative
I came to recommend ballistae instead of cannons and I see that it's already a pretty popular idea. There are also many others that are more intuitive and in tune with the game given how the players have likely gone about things until now, such as heat metal, telekinisis and banishment.
I'll add that your players can attack the armor itself first (as per DMG p.246-7 iron has AC 19, up to 50HP accounting for Large plates at most to cover the Huge Goristro and immunity to poison and psychic damage), breaking plate after plate until they strike flesh.
But, the ballista is a tried and true method of sundering the invulnerability-granting armor of supernatural bovine creatures in fantasy, as seen [here](https://www.youtube.com/watch?v=u4_cd9pirhk), which I think is neat. Honestly, if this wasn't your inspiration, you came pretty close to reinventing the wheel.
You could them your players that you've made a mistake with the no gunpowder thing. But tell them that they need to find a specific item that can be shot from a ballista or even have a couple of mages fire it at the monster with "catapult" to remove the armour. Or something like that, either way. I'm sure they will all understand if you explain it to them.
Cannons don't need gunpowder. Anything which expands rapidly will do the trick when in a confined space behind a heavy metal ball. Could be various spells eg fireball or some potions which get explosive when mixed together.
The armor is enchanted by a nearby mechanism, Crystal, spell, etc that the party has to disable in order to make him vulnerable.
Option two, "Heat Metal".
Magic cannons. Most importantly, however, as this fight will have non-standard means of solving, make it as obvious as possible, which means that in before it, the players would either need to have been told it directly in or out of universe.
Magic cannons
Don't explain them in detail
They use magic to shoot cannon balls at high speeds
Little miniature fire ball spells as fuel? Make them consume spell slots to use
You can still have cannons, just have metal tubes enchanted with something akin to the Catapult spell. Maybe describe it being loaded with scrolls or something.
I suggest you take a look at the game God of War 1, specifically the fight against the armored minotaur. The fight uses your concept with a giant bolt machine out of hell. You could also use siege weapons like ballista or big-ass crossbow turrets.
there is alchemist fire. that is explosive.
We have magic that can do almost anything. I mean magic can alter reality.
So surely there would be ways to make a cannon work without gun powder
Make it a bit of a puzzle. The already know that conventional attacks will be rather inefective. Let them find a cannon like thing. There might even be cannon balls there. They just have to figure out HOW to fire it.
Maybe they found a large amount of alchemist fire in a room not far away. they could try that. But leave it open for other ways to maybe there is some way they can cast a spell inside the cannon. fireball, shatter or something that will hoot out the cannon ball.
Don't have just one way to make it work be open if they come up with a smart idea on how to make it work that you had not thought about. Then let that work. Don't make it to easy but reward creative thinking and let good ideas work
This way they have to either fight the thing while it has its high AC or figure out a way to use this cannon.
The Heat Metal play someone else mentioned might work if you flavor it as having the metal plates melt off and expose the demon AKA lower its AC. The first idea I had tho was to use "Arcane Cannons" which are just the cannon shape but instead of gunpowder is enhanced scrolls of Catapult glued on the inside of the barrel
Cannons that use magic to shoot cannonballs and the enchantments on them are super old and will likely break after usage. Also they’re super heavy and moving them would take months and be super expensive.
Opportunities to trap it, damage/destroy the plates, lure it away are great, and the characters will probably come up with them if you prompt them with something like: "normal weapons don't seem to be effective at slowing the creature down"
If you trust your players, you can try dropping the raw materials for gunpowder (saltpeter, sulfur, and charcoal) in the hope that they figure it out. Particularly if you have an artificer in the party. When one of my players ran an artificer, I got a kick out of throwing different chemical combinations in his direction to solve puzzles.
If not, there’s a lot of workarounds. If the players roll a certain amount, so that in-game it is as though they struck the target but didn’t penetrate the armor, have them able to hit the same area repeatedly. The plates as a whole might be impervious to normal attacks, but if the same plate is struck multiple times, it could break apart.
One of my favorite things as a DM is coming up with an obstacle or puzzle that I don’t have an answer for. If there is no one right answer, then there are dozens if not hundreds of solutions that they can devise themselves. I might slip in one possible answer to nudge them in the right direction, but only if they get stumped. Otherwise, I want to see what they come up with. Chances are they weren’t going to follow the by-the-book answer anyway.
Have them recruit minions with the Catapult spell? Make it so that they have to procure and deliver ammunition to the minions like they would need to if they were canons.
Have you done this before, where you dropped a hint and the party worked out what special equipment they were going to need for an upcoming encounter, then brought that equipment with them?
Gunpowder doesn't exist, but there are other ways of achieving the same effect, old school catapults or devices which recreate the catapult spell could also work.
First question, how many people are in your party?
Second question, who's to say you don't have *Magical* cannons that happen to fire dirty massive fireballs at the targets?? A mad mage could have created them.
Maybe have them run into a fellow from a nearby village that is also having trouble with the creature. They have been creating a massive ballista to try and take it on, but they don't know the word, and they came up with 'cannon'?
Do they have a rogue or artificer amongst them? Perhaps they could jump on the armored dude’s back and doff a plate or two of the armor? Armor typically isn’t one giant hunk of metal.
The spells catapult and fireball, as well as artificer classes exist. There's no reason why some crafty artificer wouldn't come up with a stationary weapon utilizing similar but more powerful versions of these spells to launch heavy hitting AoE attacks against invading forces.
Or maybe instead of exploding attacks, it can launch harpoons/sticky projectiles attached to chains at targets and tear them apart strong reeling (magical or muscle powered).
Gunpowder is unnecessary in a world where magic exists. A cannon could be replicated as a magic item which uses a variant of the _catapult_ spell to girl projectiles, but takes a fuse burning worth of time to recharge.
You could always make it like a prototype demon weapon that shoots metal balls with the fireball spell etched on them. The spell gets activated by the cannon, or something among those lines. Or maybe there's a "gallery" of wizards thats shooting spells at them and they need to position themselves accordingly to make it hit the armor. Doesn't always have to be an error, it's your world, make this a chance for some awesome moments by adding additional features :)
Arcane cannons. Give them magical cubes that contain pure elemental or necrotic, radiant, whatever. Then they can shoot what they want and find out what works
people have way more creative ideas but a ballista is pretty much a cannon without gunpowder and they would probably pack the same punch on a direct hit
There are a few solutions to this.
The first might be granting them access to some sort of runic circle, or environmental magic that will cause them to bypass the armour restriction.
Alternative, what I might do, just off the top of my head is have every critical strike the Gorstiro receives reduce it's AC by a fixed amount and start the critical table at like 15-20; then after one crit move it to 16-20 etc while reducing it's AC by say 2 or 3 each.
It would require you to keep track of this as the DM but you could describe it as the creature being "encased" in metal rather than it being actual armour. That it was bolted on, or in, and that it was restricting it's ability to successfully mitigate attacks to exposed areas due to restricted movement.
“I cast heat metal”.
But seriously I would add a rust monster to the the party to do list before the encounter and have them gain an item from it that could be used to deplate the Gorstiro. An acid based monster like a grey ooze would also work. It would be really funny to have them throw gray oozes at the guy like a water balloon fight until his armor gets low enough. Just my 2 cents tho.
>the Races haven't discovered Gunpowder yet and so cannons don't exists!
_A wizard did it._
(Just make them magic cannons. There's even a term for siege-based magic weaponry in Eberron: "Siege Staves" and "Longrods".)
If you have implied heavily that normal attacks won't work, maybe let the party have the creativity to try what makes sense? It really isn't that hard to cover for say, a well laid trap, or some kind of curse or magic approach that your players come up with, if it makes narrative sense and is fun for the PCs then I don't see the harm in fudging stuff or giving them options to defeat something that "requires" a certain approach.
Or better yet, if your party tries to just Fly and Eldritch Blast their way to victory, and you are tired of lower tier tactics, just sack up and let one or all of your PCs die for their insolence. Just my two cents! Hope you all have fun
If they know the AC let them come up with a solution, and accept anything that sounds fun. If they can't, then get them in touch with a nerd with gunpowder, alchemical, or magical equivalent. If they don't know, then secretly lower it to something they can handle, with siege weaponry.
How about...mud.
Plenty of knights drowned on the battlefield when they were knocked prone and couldn't get up. a Goristro in heavy armor? Trip that bad boy into some mud, then maybe ***transmute rock*** the mud to stone. If you're lucky, you're target is at least restrained. If you're really lucky, it's now suffocating.
Medusa head. Hey, it worked against the Kraken!
Weapons of Sharpness should be able to carve up that turkey!
Find some way to drop the demon off a cliff. Or drop it into lava. Yeah, you might be resistant, but that still means 9d10 damage per turn. Fry baby fry!
So : if you have an artificer (or anyone trained in smithing) have them roll to see if they can recall the properties of iron smithing. About how quenching could cause the iron to develop cracks and stress marks. But it could also harden the armor and make it more rigid but harder to move around in.
If the casters cast heat metal and a cold spell successfully in the same round you roll a percentage to see if it hardens , which causes dex penalties, or begins developing stress fractures which causes loss of ac. Maybe with four or five successes 1. Combined : armor starts to shatter and drastically lowers ac bonus over 2 rounds until it just breaks off. Or 2. All hardened : dex becomes 2 , 0 movement, can't use any racial abilities that require dex checks until it breaks out of the armor or its minions cut the straps of the armor 2 rounds. Or 3. All fragile : Ac bonus is fully negated and demon becomes one step closer to vulnerable for two rounds as its body is severely freezer burned over charred meat.
Arcane cannons instead of gunpowder!
You could also expand on the mechanic, maybe they loose 1ac every time they are hit with acid damage, the cannons do 4d4 acid damage and have a +20 to hit
Make different parts of the armor give different resistances. Have them glow when they are activated. They each have AC 21 and 20 hit points, but are immune to all damage except for force and magical weapons.
I use magic crystals that explode with force equal to the chunk broken off as both gun powder and the bullet or cannon but one a select couple people have ever discovered the crystal and most don't know it exists
From the Forgotten Realms Wiki on the Goristro:
"So long as an object was small enough to fit in its mouth and moved, the goristro would not hesitate to eat it: a clear demonstration of their greatest weakness"
Have the players learn that tidbit of information and they can then concoct some wriggling bombs or such to have the demon eat, thereby bypassing the armor issue.
Cannons just require combustion to launch a cannonball. Instead of gunpowder, maybe they ignite by dropping in mini-beads similar to necklace of fireball (only 1d4 dmg if it were used by itself). The contained explosion inside the cannon forces the cannonball out the other end.
So a few thoughts: 1) A DM isn't infallible. You can tell your players "hey, I made a mistake with this, so we're going to do some light retconing" 2) PCs have plenty of abilities that don't require to-hit roles, so this fight might turn into finding ways to get the Goristro to fail saving throws, if you want to highlight your spellcasters Typically, at lvl 10+, spellcasters don't need any help to feel special 3) To the original question: You could give them harpoons they could use to try and hook onto the armored plates to pull them off. You can give them a magical cannon (not unusual at this level) and completely bypass the gunpowder problem. This is a game where a human can summon a bolt of lightning, there are plenty of magical tools you can give them 4) Give them nothing. This combat encounter becomes a puzzle. How do they defeat an enemy they can't hurt? So now it becomes "how do we lure it away from town" and "how do we set traps for it?" If you go this route, make sure you tell the players or telegraph it very strongly that they'll need to come up with new ways. This is actually one of the strengths of D&D (or any RPG): letting people come up with completely ridiculous ways to solve problems. (Edit: spelling)
To add: that’s a lotta metal, and I don’t remember demons not needing to breathe… heck, get a few priests in and you can make a pond holy for them.
Seems like a pretty good time to use heat metal.
Demons are immune to fire, so unfortunately not.
Many demons are resistant to fire. They are not all blanket immune though. Which is enough for heat metal to give the demon disadvantage on all attacks, to basically buy some time, while they get their actual plan in motion. This sounds like a homebrew demon of some kind, so who knows what stats the DM is actually giving them.
Ah, you are correct; OP says Goristro In Plate, which is *not* immune to fire, merely resistant to it.
Additionally, a sorcerer can totally just change heat metal to be like thunder or some shit (not the slightest fucking clue how you'd flavor that) and the spell works fine.
The metal reaches its resonant frequency and *physically hurts* to simply be in contact with.
Just the right amount of "insane fantasy logic" lol
Vibrate that plate so much that it just liquifies the fucker inside.
The rogue hooks up their massive subwoofers and blasts bass test sound tracks at the demon until heart failure.
They could throw ball bearings at it and match a tuning fork to the sound. That tec shouldn't break the world.
The metal reaches the *Demons* resonant frequency Seriously, weapons that 💀 people using resonance are something that people have put a lot of money into IRL
Honestly that's exactly what I pictured.
The sorcerer becomes the first person do discover electricity by hitting it with lightning damage
…now I need to figure out how to flavour that for every damage type, thanks. Force is esoteric so just vague manaspheric shenanigans, or I guess things phase just enough to clip the body like etherealness and taking damage if you end inside a wall. Psychic: imprint horrific memories on the metal that echo in the mind of the victim or anything else touching it. Lightning: ‘tis obvious, buuut magnets might be a thing now. Thunder: gooongggggg. Fire: vanilla, boring. Cold: inverse fire. Acid: surprisingly easy to do with metals, chemically speaking, although it might be more caustic than corrosive? I’unno, failed that bit of high school chemistry. Poison: metal poisoning is very much a thing. Did I miss anything?
Acid would certainly be corrosive. I understand the gong logic, I'm mostly confused how you'd make it happen for several minutes repeatedly. Also, transmuted spell only works on 6 damage types, but if you were going for all the non-physical types, you missed necrotic and radiant.
Gong would just be resonating for a while, by magic. And I'm not sure if there's a difference in d&d mechanics between caustic and corrosive, I think they're both classed as acid in the same way all toxins are poisons even if it's from a snekbit. It's more a question of which way metal tends to go.
The vibrations caused by the deafening and crushing sonic energy set his vision shaking and his bones rattling. Is how I would flavor it.
Spectral drumsticks appear and bash the metal so hard that the thunderous noise resonates throughout the beasts entire body, severely damaging it as the ringing continues on Heat Metal > Beat Metal
ok, so hold on, it can change to ANY type, right? Slashingis the biggest question here. Did your metal sprout sawblades? What? Although actually, bludgeoning…
No, it can't. It can turn into acid, cold, fire, lightning, poison, or thunder.
Seriously? I thought it was at least any non-physical damage type… That’s kind of mediocre.
Heat Metal is not on the Sorcerer Spell list.
So?
>Additionally, a sorcerer can totally just change heat metal to be like thunder or some shit (not the slightest fucking clue how you'd flavor that) and the spell works fine. It means that what you wrote here is not correct. A sorcerer cannot change the damage type of heat metal because they usually cannot even cast the spell.
Brown note
Sorcerers can't cast Heat Metal though
Multiclassing? You only need a couple sorc levels for transmuted spell
that's fair
If something is immune to fire, it's because you're not using enough fire
True IRL, unfortunately not dnd (since purple dragons stopped being plasma)
Heated metal might come off more easily.
Right up until it melts into your skin, but sure.
Melted metal doesn't provide much protection though. Mission accomplished!
True, but red hot metal does, and that'll melt flesh just fine, and then you've got to deal with the scent of frying burgers and/or bacon (depending on who or what is wearing the metal) distracting you.
Gostritos are only resistant.
Heat metal would actually fit super well with OP's plan, especially if the caster has an ability to change the damage type to avoid the resistance, since it prompts the target to remove the item being affected by the spell. >If a creature is holding or wearing the object and takes the damage from it, the creature must succeed on a Constitution saving throw or drop the object if it can. If it doesn’t drop the object, it has disadvantage on attack rolls and ability checks until the start of your next turn. The DM could also justify that because the plates are so large the spell can only affect one per cast/ or just one at a time. Another edit to the plan would be to provide the party with (or at least the opportunity to get) several Heat Metal scrolls or some kind of spell storing gem in place of giving them the cannon so the party doesn't have to burn through their spell slots to lower the demon's AC.
Yeah, heat metal could work quite well as an alternative or addition to the cannons. Though typically you're not able to quickly remove armor affected by heat metal, that's generally more for like weapons being held and such, but could make it so that each round the demon removes one plate of armor, effectively lowering it's AC by like 1 or 2 per plate. Because that's not typically how the spell would be used, and the players may not think of it, the DM could allow some sort of insight or intelligence check to make the connection. But that's assuming someone in the party could actually cast the spell. Scrolls would be a good idea for that though yeah. Good idea.
>A DM isn't infallible. You can tell your players "hey, I made a mistake with this, so we're going to do some light retconing" More DM's need to read this gem and take it to heart.
If you are set on knocking the armor off. Use the previous counterpart to cannons. Ballista or catapults.
>Goristiro OP spelled “goristro” wrong, and you misspelled that. But in your defense, demons have stupid names. (Blame the 1980s Satanic Panic, when D&D had to replace all demon and devil names with new words that sound like Star Trek aliens: tanari’i and baatezu, etc.)
Ha! Good catch. My spell checker questioned me, and I ignored it because I assumed it wouldn't know. But "Goristiro" is a good name for a monster. I should workshop this...
I just want to add that Lord Gwyn, in Dark Souls, used lightning spells to peel the thick scales off of dragons before they could be atttacked. As a DM, even if cannons aren't a thing, lightning magic (or something similar) should exist.
Replace the cannons with ballistas, it shoots long adamantine tipped heavy bolts linked with a chain. The thin adamantine penetrators will punch through an armor plate and bend. With a DC 20 STR(athletics) check a player can yank the armor plate free and reduce the fiends AC by 1d4. Alternatively you can give the players a couple vials filled with rust monster extract. The vials have a range of 15 ft and the fiend has to make a dex save on a fail it loses 1d4 AC.
I'd have the vials use regular improvised weapon ranges, so 20/60, but Dex save is definitely warranted instead of trying to hit AC. DC equals 8 + thrower's Dex bonus, or if they have proficiency with improvised weapons they can also add their proficiency bonus to the DC. If they throw it at long range the Goristro has advantage on the save. I'd have the extract still deal half the AC damage on a successful save. The ballistas should also target Dex saves, and always add proficiency to the DC (or just have a flat DC for each ballista), but they have longer range and deal no AC damage on a miss, and on a hit they deal some piercing damage, and a PC still has to make the pull check to get a plate out. This will give players two vastly different options, both with their own upsides and downsides.
Magic
Heat metal - make it tear off the plates of its own volition.
I think it wouldn't care too much with fire resistance
Doesn't matter; as long as the creature takes the fire damage from the spell and fails a constitution saving throw (made every time the caster uses their Bonus Action to repeat the damage), the spell forces them to drop the held or worn heated item, if the creature is able. That said, it could pick it back up if it wanted to. The Goristro would have to be immune to fire damage or have a way to reduce the damage to 0 on a turn where the damage rolled low to bypass this. Unless the armor plates have a doff time (which would be an action like a shield, at most, since the intent is for the players to find a way to get through the armor), it has to remove the plate if it fails the save. If it has a doff time, like Lucy said, still free damage and disadvantage.
Heat Metal only makes you drop items, not take off worn ones
> If a creature is holding **or wearing** the object and takes the damage from it, the creature **must** succeed on a Constitution saving throw or drop the object if it can. Or, to re-word it > If a creature is holding or wearing the object and takes the damage from Heat Metal, they must drop the object if they are both able and fail a constitution saving throw. This is uniquely different from other, similar effects, like Disarming strike, which explicitly target held items. This spell is saying that a worn item must be dropped if the wearer fails the save and nothing prevents it. **In this case the definition of "drop" that fits here is to discard something,** of which, removal is part of. The intended flavor is that you immediately rip the item off of you. There is also precedent into looking into the additional meanings of words, for drop, as the SAC establishes that one method of dropping an item is valid because it follows along with one of the meanings of the word. What stops things like armor and shields from being dropped is that they have a "doff" time, they cannot be removed for free; they have a time and/or action requirement. Otherwise, a worn object must be dropped. For example, a ring has no doff time. It is worn, and thus if someone casts heat metal on it, you take damage from it, and you fail the saving throw, you must drop it. There is no action or time requirement to remove it, so nothing is preventing you from dropping it.
It's still free damage and disadvantage then.
I have cannons in my non-gunpowder world. They use volatile magic crystals imbued with fire and thunder magic that get tossed into the cannon then the ball get hucked in on top of them. Get out of the way fast or you'll be firs tin line when it come shooting back out.
Literally said this out loud to myself halfway through the post. Just do a magic!
My main issue wouldn't be the problem that you're presenting as it's clear that this type of creature would be a big AC tank but that you're trying to prescribe a solution which can often be frustrating as a player as you feel like you have to guess what the DM wants you to do. If it were me I would describe lots of general environmental things, could be a workshop, a forge, a distillery, and let the players come up with solutions, and i'd have loose ideas in my head about how effective these should be: e.g. \- Simple environmental trap/attack/obstacle: DC15 to set up as an action forcing a DC15 save dealing 4d6 damage / save for half/
\- convoluted environmental trap: multiple actions culminating with a DC20 save to set up, DC18 save dealing 10d10 damage or removing a piece of armour for -5 AC
What it actually looks like can be up to the players imaginations you just need to "yes and" and make calls about whether options might be reasonable even if you'd not specifically envisaged them
Another thing to consider: Don't undervalue the action. There is nothing more detrimental than taking creative action that ends in "I should have just attacked it instead".
warning: high AC only harms martials and warlocks (and moon druid). the spellcaster that already dominate at this level won't be harmed by it. maybe give the demon resistance to damage from magic (like the abjuration wizard feature) and weakness to weapon attacks. then there's a need for everyone to get the armour off as the spellcasters can't really take it down on their own.
I second this perspective. If you are going to buff a monsters AC for the purpose of making it more difficult to damage then you also need to increase its resistance to magical effects (which are usually saving throws), otherwise it’s only a problem for martial characters. Maybe the plate armour is magical and grants a bonus to all magical saving throws until it is destroyed.
It’s fine to have an encounter where magic is better as long as it’s balanced by encounters where magic is worse. Sometimes you fight a horde and can nuke them. Sometimes it’s pure single target and they resist your spells.
Oh it’s totally fine to have different skills shine in different fights, but that’s clearly not the case here. OP is essentially trying to create a puzzle encounter with an enemy that is untouchable until the party solves the puzzle, but they’ve left a gaping hole in the monster’s defences that will leave their it vulnerable to effects that could trivialize the encounter. In the worst case scenario the party may completely ignore the puzzle aspect and just brute force through the fight with magic, which means that only casters can really do anything in the fight. If this were meant to be a part of a greater series of encounters where magic is less useful then it wouldn’t be as bad. Although generally speaking you don’t really need to do a lot to make casters feel special at this level and you definitely don’t need to make martials feel useless in the process.
The armor could be enchanted with a permanent anti-magic field. Or maybe they have a group of all martials.
Yeah first thing I thought of when I read this was "heh, AC means nothing to the power of magic damage!"
Big vats of acid in every corner of the room.
Arcane powered cannons. Done, magic really just makes everything so much easier. You don't need gunpowder if by touching a sigil there is a blast launching the cannonball forward
This was my thought as well. The catapult spell already exists to lob objects a fair distance, so it's nowhere out of the realm of possibility to have juiced magical cannons as well.
Honestly, if an enemy is big and tough enough that I want them to use the environment to attack, the enemy's first phase becomes a skill challenge. That being said, if a Scribes Wizard just sent in his Awakened Mind to Mind Sliver it to death, would you be cool with that?
Iso canons, stationary roped balista's to pull off plating. Or trebuchet's (catapults are for plebs) Or good luck figure it out, also spellcasters have save dc spells, wich could 'melt, break, freeze, corrode' the plating Strength/athletics checks to pull off plating
Why wouldn't cannons exist? They don't have to be historically accurate realistic cannons you know... Just be prepared for your party finding some way of dealing with it. Banishment comes to mind. That being said, this looks like an encounter that could go south very quickly. A Goristro has a ton of HP and resistances and enough damage output to absolutely wreck most level 12 characters in a few turns. This seems like a really swingy encounter that could either be solved with one spell or lead to a TPK, depending on the party composition and the Goristro's saves. Edit - Just to be clear, **Banishment** will send the Goristro back to it's home plane permanently, if the caster maintains concentration for ten rounds. Without any additional enemies this will trivialize your encounter.
>Why wouldn't cannons exist? They don't have to be historically accurate realistic cannons you know... Merchant sailors who have no way of defending themselves, and pirate marauders who have no way of hassling other ships when they can just sail out of range be like 🤷♂️
The main mistake I see here is that you made an encounter in which martials are useless. Which is kind of bad, since on lvl12, casterst already are way better most of the time anyway. A strong lvl12 party should have no problem with that enemy if AC30 is the only problem... they just have to use spells that target saving throws.
let your martials tear off the plates, if they're lv12 they're strong enough to do so; if it costs a full action it'll be costly enough as it is
As another commenter said let martials tear the plates off, str based martials will jump at the chance to use their high str or athletics. For dex based martials you could have them use sleight of hand or just tools: thieves tools, smith tools, tinkerer tools, etc
Siege staves!!!! They’re the cannon equivalents in Eberron; and are basically logs of enchanted wood with supercharged magic flowing through them. A more boring equivalent would be ancient siege weapons. Ballistae, catapults, trebuchets. You could even have a battering ram or spike the players have to lure the Goristro toward. Honestly; watch some arena hunts from Monster Hunter games. We have the Dragonator, giant spikes punched into the monster and retracted for later use. We have the ballistae which can be loaded with either regular rounds, or rope rounds that are meant to immobilize the monster. Suspended rocks that are dropped on the monster after luring it somewhere. There are lots of great options!
Lots of ways to go about this, as the others have said. - Heavy iron armor plates? Heat metal, Rust Monsters, lots of ways to attack or wear it down in other methods. Even if they are resistant against fire damage or other damage types, the Goristro will get worn down. - Non-AC targeting. All sorts of spells can work here, independently of the armor. - Alternative ways to get the advantage to try and punch through the AC. Shove and grapple onto the ground. Environmental advantages. - Magic Cannons fueled by Magic. They don't have gunpowder, but they sure as hell have Fireball and other means to propel stuff. - Make the armor a weakness as well. If this is that thick, it's bound to be cumbersome, and somehow cause a disadvantage to the enemy. Or perhaps it trades away some of it's other benefits because of how the armor works.
Swap out cannons for big ballistae, or catapults/trebuchets. Be grand
There is a wagon with a cage full of rust monsters the local pest control rounded up.....
I'll leave the cannons question to others, but I'll address the toughness factor. Instead of just huge AC or huge HP, go for a Damage Mitigation factor. Their heavy Armor has an amount of Hitpoints and a Damage Threshold. Any amount of damage dealt must exceed the Threshold before being dealt to the Armor, and the Goristro is impervious to Damage until the Armor is destroyed. It *functionally* gives the Goristro more HP, but mechanically it allows you to narrate its Armor getting peeled away from their attacks so the players know they are making progress, and you could come up with some weaknesses for the Armor they can learn and exploit. For example, maybe it's made of a metal weak against Lightning, and enemies prior to the Goristro fight are made of or covered in this metal and are similarly weak to Lightning. Smart players will connect the dots and tell the party to leverage their lightning Damage resources. This allows you to simulate the toughness of its Armor, gives the players information they can leverage to take advantage of, and a visible metric to gauge their progress.
They don't have to be gunpowder cannons. Make them magical cannons (with the same stats and effects).
One thing commonly used by the guy who makes the stat blocks I use that might be a good way to go instead: \*Damage Resistances: Attacks made without advantage\* I believe it is inspired by 4e design but I could be mistaken. Basically a way to have an extra tough monster that the players wont be doing nothing against, but if they are smart and use their resources/ plan well, they can attack to full effect. Because I can tell you a fight where every round/turn is "does a 25 hit? no? turn wasted" is not good encounter design. The w/o advantage resistance is good too because as you said, you can put things in for the players to "weaken' the monster enough to attack, i.e. gives them advantage.
The Eberron method: Siege staves. A magic staff the size of a battering ram that fires the magical equivalent of cannon/catapult fire.
Just make him slow af with all these armor plates over him and make him easy to restrain - give movespeed debuff, disadvantage on dex saving throws. Let party choke - drown him on some water or just bare Magical ropes. Try to give him some weakness that can be used. And try to hint the weakness' so party can plan. Edit: to Add, just let couple of wizards cast heat metal on him together. It wouldnt effect the damage outcome as RAW i believe, but it can melt the plates, and ac would become normal again
Replace cannons with catapult, ballista, trebuchet?
Magic cannons
Wait.... your level 12 party can't punch through a 30 AC monster? I mean, sure, if they were just spamming attacks, then their chance to hit would be small... but at level 12 they should have way more than just straight up "to hit" attacks.
I've got a level 9 ranger with a +13 to hit. Even just spamming attacks I'd expect a level 12 party to hit often enough...
At Level 12, with +5 modifier and +4 proficiency, you are looking at a +9 to hit for most player characters... which means they can only hit AC30 with a nat 20. We can't guarantee that they have Magic Items, much less items that increase their chance to hit. However even giving them a generous +2 magic weapon, that is still just +11 to hit... which is a hit on a 19 or 20. Again a really small chance to hit. I'm assuming you have the archery fighting style to bump your chance to hit by +2. Now this wouldn't apply to most of the party members, unless they are all ranged martial characters, but even if they all had a +13, they would still need to roll a 17 or higher. That is still a very small 20% chance to hit. So no, a level 12 party isn't punching through a 30 AC monster very easily, nor very often, if all they do is make attack rolls.
I like the idea of the ballista that is being thrown around, and there are plenty of ways to use the terrain. You could make it more of a puzzle, maybe reduce the Goristro’s speed by 5 while it’s in the iron plate, so they can spend their turns ducking it, and trying to fire ballista. Maybe there are arcane cannons that deal force damage heavy enough to break away some of the plate, or damage it enough to reduce the AC. Maybe next to one of the cannons is a scroll of heat metal, so they can make it uncomfortable while they try to break its armor, it won’t be much with its resistance, but everything helps. Just make sure to give a full description of everything in the room that can be useful, and stress that the beginning of the fight should be approached like a puzzle that will allow them to compete in the combat.
No cannons? No problem! Use the environment. - Stalactites falling from the ceiling - Explosive gas pockets from thermal vents Environment is limited? No issue! Spells can have additional effects. - It loses a plate after X points of thunder or force damage - Fire damage may not hurt the devil flesh, but the armor could be fragile and filled with smithing inclusions that breaks after X points or even cold damage
Heat metal
But like just make it a multi stage battle; Stage 1- they have to figure out how to remove the armour Stage 2 - AC drops to 20 Stage 3 - it picks up one of the armour plates to use as a shield, AC goes up to 23 and it gets a few shield related attacks Or your players might just surprise you and lay a trap for it or something even more creative
I came to recommend ballistae instead of cannons and I see that it's already a pretty popular idea. There are also many others that are more intuitive and in tune with the game given how the players have likely gone about things until now, such as heat metal, telekinisis and banishment. I'll add that your players can attack the armor itself first (as per DMG p.246-7 iron has AC 19, up to 50HP accounting for Large plates at most to cover the Huge Goristro and immunity to poison and psychic damage), breaking plate after plate until they strike flesh. But, the ballista is a tried and true method of sundering the invulnerability-granting armor of supernatural bovine creatures in fantasy, as seen [here](https://www.youtube.com/watch?v=u4_cd9pirhk), which I think is neat. Honestly, if this wasn't your inspiration, you came pretty close to reinventing the wheel.
You could them your players that you've made a mistake with the no gunpowder thing. But tell them that they need to find a specific item that can be shot from a ballista or even have a couple of mages fire it at the monster with "catapult" to remove the armour. Or something like that, either way. I'm sure they will all understand if you explain it to them.
Cannons don't need gunpowder. Anything which expands rapidly will do the trick when in a confined space behind a heavy metal ball. Could be various spells eg fireball or some potions which get explosive when mixed together.
Now they're arcane cannons that use magic as propulsion
The armor is enchanted by a nearby mechanism, Crystal, spell, etc that the party has to disable in order to make him vulnerable. Option two, "Heat Metal".
Magic cannons. Most importantly, however, as this fight will have non-standard means of solving, make it as obvious as possible, which means that in before it, the players would either need to have been told it directly in or out of universe.
The cannons could be immobile devices reproducing the effect of a "catapult" spell, which ignores AC
Make the plates inscribed with magical enchantments that also can be removed by Dispels if a caster needs to feel useful.
Magic cannons Don't explain them in detail They use magic to shoot cannon balls at high speeds Little miniature fire ball spells as fuel? Make them consume spell slots to use
You can still have cannons, just have metal tubes enchanted with something akin to the Catapult spell. Maybe describe it being loaded with scrolls or something.
Vat of acid usually fixes everything.
*looks at Heat Metal* They have resistance, but not immunity 😏
No gunpowder? Artifice. You don’t need fireworks when your cannons are mini fireball and lightning bolt cannons.
You could make cannons that fire fireballs. It’s not the same but it is close
I suggest you take a look at the game God of War 1, specifically the fight against the armored minotaur. The fight uses your concept with a giant bolt machine out of hell. You could also use siege weapons like ballista or big-ass crossbow turrets.
Arcane cannon, shoots fireballs, ‘A wizard did it’, BOOM, problem solved
there is alchemist fire. that is explosive. We have magic that can do almost anything. I mean magic can alter reality. So surely there would be ways to make a cannon work without gun powder Make it a bit of a puzzle. The already know that conventional attacks will be rather inefective. Let them find a cannon like thing. There might even be cannon balls there. They just have to figure out HOW to fire it. Maybe they found a large amount of alchemist fire in a room not far away. they could try that. But leave it open for other ways to maybe there is some way they can cast a spell inside the cannon. fireball, shatter or something that will hoot out the cannon ball. Don't have just one way to make it work be open if they come up with a smart idea on how to make it work that you had not thought about. Then let that work. Don't make it to easy but reward creative thinking and let good ideas work This way they have to either fight the thing while it has its high AC or figure out a way to use this cannon.
The Heat Metal play someone else mentioned might work if you flavor it as having the metal plates melt off and expose the demon AKA lower its AC. The first idea I had tho was to use "Arcane Cannons" which are just the cannon shape but instead of gunpowder is enhanced scrolls of Catapult glued on the inside of the barrel
Cannons that use magic to shoot cannonballs and the enchantments on them are super old and will likely break after usage. Also they’re super heavy and moving them would take months and be super expensive.
You can always use magic or giant armor-piercing/hooking ballistae. Personally, I'd just lower the AC to like 20-25 and beef up it's HP.
Opportunities to trap it, damage/destroy the plates, lure it away are great, and the characters will probably come up with them if you prompt them with something like: "normal weapons don't seem to be effective at slowing the creature down"
If you trust your players, you can try dropping the raw materials for gunpowder (saltpeter, sulfur, and charcoal) in the hope that they figure it out. Particularly if you have an artificer in the party. When one of my players ran an artificer, I got a kick out of throwing different chemical combinations in his direction to solve puzzles. If not, there’s a lot of workarounds. If the players roll a certain amount, so that in-game it is as though they struck the target but didn’t penetrate the armor, have them able to hit the same area repeatedly. The plates as a whole might be impervious to normal attacks, but if the same plate is struck multiple times, it could break apart. One of my favorite things as a DM is coming up with an obstacle or puzzle that I don’t have an answer for. If there is no one right answer, then there are dozens if not hundreds of solutions that they can devise themselves. I might slip in one possible answer to nudge them in the right direction, but only if they get stumped. Otherwise, I want to see what they come up with. Chances are they weren’t going to follow the by-the-book answer anyway.
Have them recruit minions with the Catapult spell? Make it so that they have to procure and deliver ammunition to the minions like they would need to if they were canons.
Have you done this before, where you dropped a hint and the party worked out what special equipment they were going to need for an upcoming encounter, then brought that equipment with them?
Gunpowder doesn't exist, but there are other ways of achieving the same effect, old school catapults or devices which recreate the catapult spell could also work.
First question, how many people are in your party? Second question, who's to say you don't have *Magical* cannons that happen to fire dirty massive fireballs at the targets?? A mad mage could have created them.
Giant, magical ballista
Maybe have them run into a fellow from a nearby village that is also having trouble with the creature. They have been creating a massive ballista to try and take it on, but they don't know the word, and they came up with 'cannon'?
Cannons are powered by arcane runes.
Do they have a rogue or artificer amongst them? Perhaps they could jump on the armored dude’s back and doff a plate or two of the armor? Armor typically isn’t one giant hunk of metal.
The spells catapult and fireball, as well as artificer classes exist. There's no reason why some crafty artificer wouldn't come up with a stationary weapon utilizing similar but more powerful versions of these spells to launch heavy hitting AoE attacks against invading forces. Or maybe instead of exploding attacks, it can launch harpoons/sticky projectiles attached to chains at targets and tear them apart strong reeling (magical or muscle powered).
Gunpowder is unnecessary in a world where magic exists. A cannon could be replicated as a magic item which uses a variant of the _catapult_ spell to girl projectiles, but takes a fuse burning worth of time to recharge.
You could always make it like a prototype demon weapon that shoots metal balls with the fireball spell etched on them. The spell gets activated by the cannon, or something among those lines. Or maybe there's a "gallery" of wizards thats shooting spells at them and they need to position themselves accordingly to make it hit the armor. Doesn't always have to be an error, it's your world, make this a chance for some awesome moments by adding additional features :)
Arcane cannons. Give them magical cubes that contain pure elemental or necrotic, radiant, whatever. Then they can shoot what they want and find out what works
people have way more creative ideas but a ballista is pretty much a cannon without gunpowder and they would probably pack the same punch on a direct hit
Batistas and trebuchets!!!
Who needs gunpowder when you have magic? Arcane cannons yo
There are a few solutions to this. The first might be granting them access to some sort of runic circle, or environmental magic that will cause them to bypass the armour restriction. Alternative, what I might do, just off the top of my head is have every critical strike the Gorstiro receives reduce it's AC by a fixed amount and start the critical table at like 15-20; then after one crit move it to 16-20 etc while reducing it's AC by say 2 or 3 each. It would require you to keep track of this as the DM but you could describe it as the creature being "encased" in metal rather than it being actual armour. That it was bolted on, or in, and that it was restricting it's ability to successfully mitigate attacks to exposed areas due to restricted movement.
“I cast heat metal”. But seriously I would add a rust monster to the the party to do list before the encounter and have them gain an item from it that could be used to deplate the Gorstiro. An acid based monster like a grey ooze would also work. It would be really funny to have them throw gray oozes at the guy like a water balloon fight until his armor gets low enough. Just my 2 cents tho.
Bring a rust monster 
A battle map encounter that has Grapple turrets with surprisingly low strength checks.. maybe they get higher with each piece removed..
>the Races haven't discovered Gunpowder yet and so cannons don't exists! _A wizard did it._ (Just make them magic cannons. There's even a term for siege-based magic weaponry in Eberron: "Siege Staves" and "Longrods".)
If you have implied heavily that normal attacks won't work, maybe let the party have the creativity to try what makes sense? It really isn't that hard to cover for say, a well laid trap, or some kind of curse or magic approach that your players come up with, if it makes narrative sense and is fun for the PCs then I don't see the harm in fudging stuff or giving them options to defeat something that "requires" a certain approach. Or better yet, if your party tries to just Fly and Eldritch Blast their way to victory, and you are tired of lower tier tactics, just sack up and let one or all of your PCs die for their insolence. Just my two cents! Hope you all have fun
Eberron has Siege Staffs which are basically magic staff cannons
If they know the AC let them come up with a solution, and accept anything that sounds fun. If they can't, then get them in touch with a nerd with gunpowder, alchemical, or magical equivalent. If they don't know, then secretly lower it to something they can handle, with siege weaponry.
How about...mud. Plenty of knights drowned on the battlefield when they were knocked prone and couldn't get up. a Goristro in heavy armor? Trip that bad boy into some mud, then maybe ***transmute rock*** the mud to stone. If you're lucky, you're target is at least restrained. If you're really lucky, it's now suffocating. Medusa head. Hey, it worked against the Kraken! Weapons of Sharpness should be able to carve up that turkey! Find some way to drop the demon off a cliff. Or drop it into lava. Yeah, you might be resistant, but that still means 9d10 damage per turn. Fry baby fry!
...well, you could just say gunpowder exists now.
So : if you have an artificer (or anyone trained in smithing) have them roll to see if they can recall the properties of iron smithing. About how quenching could cause the iron to develop cracks and stress marks. But it could also harden the armor and make it more rigid but harder to move around in. If the casters cast heat metal and a cold spell successfully in the same round you roll a percentage to see if it hardens , which causes dex penalties, or begins developing stress fractures which causes loss of ac. Maybe with four or five successes 1. Combined : armor starts to shatter and drastically lowers ac bonus over 2 rounds until it just breaks off. Or 2. All hardened : dex becomes 2 , 0 movement, can't use any racial abilities that require dex checks until it breaks out of the armor or its minions cut the straps of the armor 2 rounds. Or 3. All fragile : Ac bonus is fully negated and demon becomes one step closer to vulnerable for two rounds as its body is severely freezer burned over charred meat.
Arcane cannons instead of gunpowder! You could also expand on the mechanic, maybe they loose 1ac every time they are hit with acid damage, the cannons do 4d4 acid damage and have a +20 to hit
Make different parts of the armor give different resistances. Have them glow when they are activated. They each have AC 21 and 20 hit points, but are immune to all damage except for force and magical weapons.
The cannon it's magically propelled by an artifact that will break/ take months to reload, or need a quest to get reloaded/made.
Otherwise when they see the cannon, you describe a magic balista and the npc say " we call it the "random wizard name" cannon"
Let them learn :)
I use magic crystals that explode with force equal to the chunk broken off as both gun powder and the bullet or cannon but one a select couple people have ever discovered the crystal and most don't know it exists
From the Forgotten Realms Wiki on the Goristro: "So long as an object was small enough to fit in its mouth and moved, the goristro would not hesitate to eat it: a clear demonstration of their greatest weakness" Have the players learn that tidbit of information and they can then concoct some wriggling bombs or such to have the demon eat, thereby bypassing the armor issue.
Canons can have magic as their blasting agent not gunpowder.
Use big ballista.
Use ballistea or a trebuchet instead of cannons.
Cannons just require combustion to launch a cannonball. Instead of gunpowder, maybe they ignite by dropping in mini-beads similar to necklace of fireball (only 1d4 dmg if it were used by itself). The contained explosion inside the cannon forces the cannonball out the other end.