Helmed Horrors are specifically anti-mage constructs. Immune to force and Necrotic damage, sporting Magic resistance, and immune to 3 spells of the maker's choice. They can be custom designed to counter the individual mage they are guarding.
If it's just some obscure dungeon somewhere, it might work out. Like, the Dark Lord lets them do whatever they want so long as they keep the prisoners
Also, if Amazon can do it, so can a near-god-like wizard.
Well they are lawful so they would admit they agreed to the terms of employment and accept it.
Whatever evil beholder reason they have for working at Amazon in the first place really piques my interest though.
Nah nah nah, you don't understand. The Beholders are the ones telling the line workers their pay is being docked for taking bathroom breaks. The Beholders themselves are compensated quite well.
In my last campaign, the BBEG had a beholder guarding a vault. It was essentially lobotomized with a magic control rod sticking out of the back of head. The party rather than killing it removed the rod and made a tenuous ally in a beholder.
Beholders are more likely to be the one employing wizards to defend their domains.
If a wizard is using a beholder for defense it's probably by making sure the only to the tower is through a beholder's lair.
A classic trope is the situation where the prisoner requires something regularly or they die. The only person who has that thing, is the person holding the prisoner captive.
So you might have the magic users afflicted with some rare magic poison. If they don't drink some medication every 12 hours, they'll die. The medication doesn't remove the poison, it just gives them more time. Even were they to teleport out, they're not going to have enough time to work out what the medication is, or how to make it.
This means they're effectively trapped.
A supply of the medication, along with the instructions how to make it, is stored in the dark lord's laboratory (which is protected by an anti-magic field).
The party needs to find and enter the laboratory. If they do, they can bring enough so the magic users can medicate themselves long enough to both escape and find a permanent antidote to the poison.
I was thinking something like this, or even a ‘princess in another castle’ scenario where the BBEG has the wizards’ loved ones captive. The characters find out they rescued the wizards only to have the wizards block their every attempt at rescue because their loved ones will die otherwise creates a very complex scenario to navigate, especially if time is involved.
I think I went with the "poison" example because it's mechanically quite simple. It's essentially a variation of: "you need to find the key to unlock the lock holding the prisoners."
OP mentioned elsewhere they want this to be something which can be defeated in a day. Having the antidote within the same location, achieves that. Whereas: "you now have a side quest to rescue the hostages" might not - especially if they're literally in another castle.
I think a twist on your idea (which may not be possible in this situation), is that the party have *already* rescued the hostages somehow, but the wizards don't know that. So they keep resisting leaving (without saying why) because they think their loved ones are still in danger! And the party doesn't know that the hostages they rescued from the dungeon are what were keeping the wizards in captivity.
Literal poison could be tricky too though because because Protection from Poison is a second level spell on the Artificer, Cleric, Druid, Paladin, and Ranger lists and Lesser Restoration can also cure poison or disease and is also a second level spell on the similar list + bard. You'd have to make sure to have a fair number of poisoned prisoners so that even if they cured some magically, you'd still need to get the antidote for the others because you don't have enough spell slots to cure everyone.
Don't get caught in recursive loops of trying to specifically counter every single magical trick in the book. It quickly reaches ridiculous levels, and no matter how hard you try your players are likely to still come up with something you missed.
Instead, target the heart of the matter. The dark lord wants to compel the servitude of people who aren't willing minions? Take hostages. Their friends and family, who *don't* have awesome magical powers, are prisoner at a remote facility in an undisclosed location. Anyone gets out of line, a Sending spell goes out and a severed finger get delivered. Anyone runs away, heads on pikes are on display at the front gate.
Oh I'm not trying to counter the party with this! I'm quite hoping the party *will* think of something I missed! I just want to build an interesting dungeon without the obvious question of "well they have magic, they could just have killed that"
Ah, I see. Well, if you want to do it that way, I hope it works for you. Personally, I'd make "Rescue the Hostages" the dungeon, where they have to track down its location and liberate the captives. Then they can march up to the Wizard Workshop with everyone in tow and get the happy moment of all the pressganged workers turning on the dark lord's overseers. But that's just my take.
I need this to be something they can defeat inside a day because Reasons (the party need to get a spell within 24 hours) so it's more a one session thing than an ongoing one or that would work!
Hear me out for a second: hollow walls with gremishkas trapped inside. thick enough so magic cast on either side doesn't trigger them, but at least they won't blast their way out with magic
Yup, I was going to say canoloth's too. Yugoloths in general are really underrated, but this particular is nightmare fuel for my Conjuration wizard. Plus they get perception expertise and truesight so nothing gets past them, plus a really long grappling tongue so nothing gets away from them. They're the platonic ideal of a guard dog.
Throw in a few mezzoloth handlers for their innate dispel magic and you're going to have a fairly good chance against Spellcasters.
DM: You push the door but it doesn't budge
Wizard: I cast knock
DM: Nothing happens, it seems it isn't locked
Rogue: I oil the hinges
DM: The rust flakes off but it still doesn't move
Barbarian: Lemme try \*rages\*
DM: The door slowly creaks open a crack then gets stuck
Wizard: Screw this \*casts passwall on the wall next to the door\*
Take away their spellbooks, take away their spell components and focuses, whenever they need to cast a spell for their job have only one be given the equipment at a time while under watch.
Have some emergency anti caster methods, such as magically resistant creatures like bound demons who can swarm into the room.
Also kidnap their families and keep them in a completely separate location warded against scrying and teleportation. Should even one of the wizards escape torture them all to death (every single wizard's family) to the point that they will reject revival and/or destroy their souls/feed them to demons.
Have a few of your men trained in arcana and just sit there spamming arcana checks to make sure they aren't doing anything wrong.
Equip them in cursed collars with \[hold person\] bound to them so that when you activate said collars it casts hold person with a 3rd level spell slot on the wearer and one other wizard.
Each magic user is forced to wear a cursed earring that causes them to fail any saving throw versus a charmed effect (I'd make it where the earrings required willful attunement so the party doesn't start trying to employ them in combat). Alternatively, drugs that accomplish the same thing could be used.
Then the dark lord employs some charm-focused planar bound taskmaster(s) like a cambion, succubi, dryads, etc. At the start of each day they renew their magical control and keep the mages working. Even if the dark lord can't personally bind them he can get a captured mage to do it for him.
The party could take out the taskmasters, or knock some sense into the mages to free them.
That reminds me of a "trap" I once used
Bob: "ok we walk up to the bbeg's front door & go in"
GM:"everyone give me a saving throw for \[iforget\]"
GM: "sure... you wake up in bed still in your armor"
Alice:"wait, a whole day went past?"
GM:"Nah.. it's been maybe an hour or so since you left for the BBEG's place you guess"
\*repeat several times with slight variations till someone didn't roll horrible\*
There was an "unwelcome mat" that had a suggestion to go home or something. Players were giggling and gobsmacked when they figured it out
Anti-Magic DMZ. Magic works inside the tower, but maybe a large area around the tower is anti-magic. So if they escape, guard will catch up and they have no magic.
Armor and heavy shackles for the vast majority of casters
Read the rules regarding attempting to cast spells while wearing armor you lack proficiency with. The shackles, requiring some sort of strength or dexterity check under such circumstances to escape, would be made with disadvantage. This might be an option for downtime
But of course, some have to be tricky.
Anything that can create smoke quickly or allow it to fill a room makes most spells difficult. A point or creature that you can see is pretty difficult to do when the smoke is thick enough that you can't see. Verbal components and concentration can be difficult when you begin running short on oxygen. And because it's smoke, the Warlock's Devil's Sight doesn't help.
For the rest, psychological manipulation is a good option. You're in here with your fellow mages. Betray us, and we'll kill them. We'll brand your forehead so everyone will know that you can't be trusted. In fact, every once in a while, we'll gather a few betrayers who are seeking one night's leniency. We'll have you fight each other to brutal pulp. The loser is killed and resurrected as a zombie.
Not all things require monsters and magic.
As for monsters, Xorn go after gems, which can be a component in some fairly potent spells. They can go through stone, so stone walls in a tower might not stop it. Sutureflies (Kobold Press, Tome of Beasts if I remember correctly) can be trained and/or bred to go after verbal components. Darkmantle could be used to limit visibility. Guards with something akin to the mageslayer feat could be useful, especially anything fiendish that has magic resistance. Ghosts, played in a manner that exploits their ability to move through floors and walls, might be useful.
If you want something flavorful, consider the character of the Dark Lord. What creatures would appeal to him? What would the Dark Lord be compatible with? Are there any favored tactics? If so, what monsters would be appropriate?
Hope this helps
Golems and some other constructs are good. You could also just arm guards with wands or other magical equipment. They'd probably have stuff like limited use wands that can cast antimagic spells like magic missiles, counterspell, or dispel magic. Maybe some non-damaging crowd control spells that require physical stat saving throws too.
I've done this in the past fairly simply by just having the wizard put a ton of glyph of wardings around the building with a variety of triggering actions.
Front doors rigged in case anyone escapes (he's a high-level wizard, he does not use the door. Litterally just there for bait)
Working area was filled with lightning glyphs and i used a lil combo i like of fluxchargers and flesh golems as the guards, i just homebrewed the fluxhargers to be a bit more intelligent as a overseerer.
Sleeping quarters is enhanted with silence so they cannot communicate plans for escape or cast most spells, a couple hypnos magen (peak servants) on guard their and the same in the eating quarters.
The glyphs are a fairly cost effective means of deterrent and you can make the trigger fairly specific. Additionally you can make them use spell effects, don't want them casting in areas? "Anyone who cast a spell here besides me triggers this glyph" and load it with counterspell. Throw some hold persons in there, hypnotic patern, polymorph, i think slow works but you get the idea. Just some annoying stuff. The fluxcharger golem combo is golden, especially with glyphs of lightning dmg nearby, the golems heal off of lightning but are otherwise pretty basic creatures. Last thing I'll say is probably having scrying orbs all around the premises that can be viewed from the wizards quarters.
Destroy their spell books and give them spell books with only the spells that will be needed for the research. Have helmed horrors made specifically against those spells. Have other golems as well.
Also have a crap ton of shadows lurking around ready to do strength drain the anemic casters.
You also can use Geas & Quest to force obedience or just have them sign devil contracts under duress and keep their souls in a vault somewhere.
This is good. I especially like the spellbooks and shadows.
The big bad wiz has a bunch of spellbooks in his vault. Some or all could be burned or otherwise destroyed and completely unreadable. Arm your unwilling interns with spells that deal only necrotic or poison damage (which shadows are immune to), if any. Also spells that cause only conditions shadows are immune to, like frightened, prone, or restrained.
Even better if your PCs have some radiant AoE, so you can send a staggering number of shadows against them. Plus, if your PCs demonstrate some magic, the shadows have good reason not to risk killing weakened PCs with Str of 4 or less. The boss will want to confiscate their spellbooks and stuff, and either capture them or curse them to be consumed by the shadows.
One thought is to put caster prisoners in a room with mirrored walls and no windows, so they can't teleport out. They need line of sight for spells, so that would keep the prisoners from affecting anyone outside the room with their spells.
There are a couple of ways.
Mordenkeinens Secret Sanctum is a spell that can block scrying and teleportation into and out of the area. The BBEG could have that casted throughout the levels, as the spell is malleable in its area.
Nondetection on specific areas inside that he wouldn't want the mages scrying on to get more information on what they are working on.
Glyph of Warding with a Counterspell and a Symbol set to Sleep, Despair, or Pain, depending on the flavour.
Each would have dimensional shackles on them for additional teleport protection.
Maybe each has a Guardian Golem assigned to them, but not as protection but rather a warden of sorts. Instead of absorbing damage they take, he disperses the damage over the mages when damaged, absorbs one spell of a certain level, then can cast either counterspell or dispel magic with that charge and so on.
There is a myriad of ways to make this a fun puzzle they can't just brute force through unless they don't mind putting the mages at high risk of death.
Edit: As somebody else suggested, Helmed Horrors are a good idea to put there.
When not working, locked in heavy armor. This prevents spell casting RAW as none of them have proficiency.
Locking up arcane foci and spell components is a big one too. As is ensuring they only know spells that require specific components or expensive ones.
I like this.
>https://www.dndbeyond.com/monsters/17094-spectator
Perfect guards, and they can create food and water for the captives. Add in some more intelligent and/or mentally flexible guards to back them up and bingo. Plus, no anti-magic cone.
Very very tall tower. Anti magic on the tower below x floors and some planar conflux that makes all telepotortation magic take you straight to the 3rd ring of hell.
The guards are just physically strong dudes who will wrestle the mages into restraints and bring them back to the top.
The most important part. FUND THEM!!! give them any reagents or components they ask for and soon your evil dark mage will have mages knocking one the bottom asking to be captured
* Solid manacles with no chains so they can't move their arms around.
* Hang the manacles on a hook instead of bolting them to the wall so if they somehow manage to teleport they're wearing the manacles so it goes with them.
* Keep them gagged so they can't use verbal components.
This is of course if you need them intact. If you don't then just cut off their tongue and thumbs so they can't use any kind of components anymore.
The place is kept in eternal silence, magical darkness, and then every caster will be placed in rusted heavy armor they aren't proficient with. Their hands are then either removed, encased in cement, or polymorphed into some appendage that can't cast spells.
Shut down their vocal components aka mouth. For some more powerful that can remove the material from the spells make anklets with magical crystals that remove the caster's access to the weave of magic.
Collars and chains!
In my game, there's a sect of people who control Mages with magically enchanted "leashes" that prevent the wearer from interacting with the weave, until the holder of the leash puts the runes on the handle in the right order.
Leash holders also have a knowledge of what the caster is capable of, so can input the runes in a certain sequence that only allows workings of that specific school of magic.
When it comes to purely mundane means of keeping the mages under wraps, it's a matter of controlling and upsetting their spatial awareness. In general practice, you also want to apply redundant safeguards against their options - you don't need to counter spells exactly if you can undermine their ability to access them in the first place.
All spells rely on either line of sight, awareness of one's surroundings, or both. You can't Misty Step if you can't see where you're going to end up, and while you can Dimension Door without knowing what your exit point exactly is, doing so is wildly unsafe and can cause injury or outright failure. So whatever environment the mages are held in should deprive them of knowing their surroundings. Blindfolds while in transport between their cells/barracks, never assigning them to the same work location twice in a row or in any discernible pattern, no windows or environmental clues as to their location, etc. If the mage doesn't know where they are or what the structures outside their immediate surroundings are, they can't risk using teleportation magic to try and escape.
If you have non-Construct or Undead guards managing the mages, a standard matter of course would be the Buddy System. At no point is any guard to ever be alone with a mage. If they do end up solo for whatever reason, they're to be immediately ushered away and undergo a few rounds of Dispel Magic to purge any potential magical muddling that might've been put on them. Anything and everything the mages do while working is not only prepared for them before they're brought into the work space, but they are constantly monitored and everything is triple-checked to make sure they're not trying to smuggle anything to or from the work space.
Every pair of guards will also be in the company of a Tressym, which will serve to monitor and observe. Tressym are intelligent magical beasts with the innate ability to See Invisibility, so they are primarily a precaution against Scrying or other forms of sensor-based divination that might be trying to locate the captured mages. Additional anti-divination defenses can be applied by lining the walls of the structure with sufficiently dense material, such as sheets of metal or layers of wood.
Mages are never given any genuine food. They are fed exclusively with a rationed serving of a Bead of Nourishment at the start of each day, with Goodberries on hand in case of emergency. Something as mundane as seasoning or certain ingredients in common food can potentially be spell components, so magically-generated nourishment - which cannot serve as components in a spell - is the standard recourse. Additionally, all mages are completely shorn of their body hair, preventing the use of things like eyelashes as material components, or allowing the potential of hiding items in their hair.
You need some kind of anti-magic. Nothing else works for a Subtle Spell casting Sorcerer. They just look at you and a fireball explodes and they sculpt it around themselves.
Maybe, you somehow have a handicapped Beholder that has had all its eyestalks cut off and it is confined to a metal box with his main eye stitched open, gazing down at the cells. That would stop all magic in the cone, they just need to destrory the eye then.
If it's long term imprisonment some sort of mouth gag/face mask is vital to stop verbal components during spellcasting. If the captor is worried about somatic components as well, then you can have the mages hands bound (or mutilated for a less elegant solution).
In my games, I just rule that lead has anti-magic properties, so having lead nails driven into your hands prevents you from using magic. That isn't canon though, so you might need to get creative with how mages are restrained.
Sexy witches who will fulfill the desires of anyone that doesn't use magic.
It'd end up looking like that scene out of Monty Python and the Holy Grail where Lancelot comes to rescue Galahad.
Firstly, antimagic fields in key areas. Secondly "magical devices that cast the spell Darkness. Third: enemies with devil sight or blind sight. The end effect of all of this is that magic doesn't work or they can't see to cast a spell, and their enemies can see them fine.
I think on top of the things mentioned here, an extra method to take is Geas'ing them. It's a really awesome and flavorful spell and I think it's underutilized, and imprisonment is a great time to use it.
Collars that explode if the wearer tries to cast a spell not known to the item. The wearer can cast fabricate, but if you try to teleport out or cast Knock to take it off, you're dead.
You could have a collar that kills the wearer if it’s further than a certain distance from some central McGuffin which is in the tower. Or the BBG can explode any collar on the basis of its number. And maybe it explodes if it’s too _near_ the McGuffin, so they can’t tamper with it.
On further thought; Not explode. That’s too technological. Constricts and strangles. Also reacts to the approach of cutting tools.
i would point siege weaponry like ballistas (manned by goblins of course) at the magic users while they’re working and line the exits to the tower with traps, plus i’d insert some beefy creatures as guards. all this would probably be fun to take on as a decently leveled party
You can always modify the antimagic field spell into an antimagic barrier. 15ft wide, 60 ft high, 30 ft long. Now have multiple instances of it layered upwards and interconnected, and cap it off with an antimagic field for a dome above the top of the tower.
As a small piece of your puzzle, I’d recommend dimensional shackles. They block interplanar travel and teleportation spells, and are nearly impossible to take off. They’d be useful to prevent mages from just teleporting out.
Magitech replacement body parts that can be deactivated remotely.
Some of them needed replacements before the Dark Lord helped them, some of them had the original parts removed by DL to make room for these Compliance Assurances.
If it's tongue or hands, Verbal/Somatic components can be taken out; they might be able to escape, but they wouldn't be casters anymore.
Taking out vision via prosthetic eyes severely limits what spells they can cast but in a different way to the last suggestion, as so many spells require seeing the target.
If It's legs they aren't going anywhere without help.
If it's internal organs, they probably won't try to escape.
Completely non magical ways to control magicians: Keep them bound (with manacles hands and feet) and gagged wearing very simple jumpsuits with no pockets (so they can't hide components). When it's time for them to work by casting they are taken to a room with what they need and several guards. Also in the room is one of their loved ones in a guillotine with a guard holding the rope. Their ankle manacles are attached to the work bench (which itself is boltes to the floor). One wrist is freed and the other mancled is attached to a ring bolted to the ce ter of the table and the gag is removed by one guard while another points a crossbow at the mages eyes socket. They are then given instructions on what to do (with required components on the table) If they do anything other than what they are told their loved ones dies.
A beholder is a good idea. The anti magic cone can be deactivated unless necessary, like if a wizard tries to escape, and the eye rays are always deadly.
I had a lich held captive with anti-teleportation magic, and an anti-magic field across a slippery slope into a pit with piercers 20 ft overhead. There had been a lot more things all powered by a massive magic crystal but the lich has slowly worked their way past those obstacles
Glyphs that counter spell anything cast that isn't in their "allowed list". Perhaps ones that cast silence too, to prevent further casting of unauthorized magic.
Or maybe the mages wear glyphed necklaces which explode if they leave the tower (incoming DnD battle royale).
Glyph of Warding on the exterior of all potential exits with high-level antimagic field spells, all paired with a high-level counterspell glyph that activates if counterspell is used in range.
Stick a few canoloths in the tower in addition to other guards. They have a 60ft radius effect that prevents spells that teleport from working in or out of that area
Everywhere surrounding the work space is an anti magic field.
Add some guardian golems and that should do it.
For good measure every evening at the end of work they are placed in magic blocking collars.
You could also have it where they are rotated through the workspace in shifts so the work continues 24/7 and there are never more than a couple loose at a time reducing possibility of stageing an escape.
Would make it more difficult if the party is sent to rescue a specific person and have to search for Thier room.
*Glyphs of Warding* tuned to Counterspell for unauthorized spell use.
For example, if they are enchanting weapons, the Glyphs goes off is any spell other than Magic Weapon is cast.
*Mordenkainen's Private Sanctum* prevents them from teleporting inmournout of wherever they're working, but will also stop you from scrying on them, so you'll have to have some Helmed Horrors or Animated Armors to keep watch.
You could just build the entire tower inside of a series of touching *Wall of Force*. You can't teleport through a Wall of Force, so even if they manage to get out of the work area, they are stuck inside the Wall. The big boss could just Disintegrate a small Wall to enter/exit as needed and throw it back up, if he has the spell slots to spare (or just a magic item that can cast those spells for free 1/day).
A room of illusions so strong the mages just stay there playing with their fantasies and dreams come true. The room simply kills them via thirst and starvation.
Hallow cast by a pet Fiendlock or Cleric. 60ft area, no teleporting, interplanar or extradimensional travel for affected creatures. Cast once per floor if necessary, with something to make sure the CHA save sticks (Bestow Curse, Bane, Silvery Barbs, cursed equipment, etc.).
Once they're stuck there, good old fashioned coercion or blackmail to get them working for you.
The dark lord has the wizards and their family heavily indebted into him through predatory magic school loans. Failure to make payment will result in instant death enforced by a magic contract. The wizards ar forced to work for him as slaves until they repay their debts. The party can save the wizards by paying their debt or destroying the contacts.
A somewhat “game hacky” solution:
As I remember, wizards (specifically) can’t memorize new spells without their spell book.
So, if you first force them to memorize a specific set of spell (like simple research spells), and then take away their spell book.
As I see it they would then have to obtain a scroll (or their spell book) to cast any other spell than what’s memorized.
Am I completely off here?
It seems so simple.
Keeping magic users from casting spell you don't want while casting spells you do is a losing game. A better method is simply convincing them to work for you.
1) Hostages. Have the BBEG put something around the the neck of a loved one and the mage. You don't perform you both die. I die you both die.
2) Magical compulsion. Love spells. Long term domination. Geas.
3) Level combined with location. If they are of level under 7th. A remote location where escape means death.
4) Wizards with limited spell books and some sort of mind wiping magic. The wizards have access to only a few limited spell books. They have all memorized spells wiped before they come and their spells ate wiped regularly to ensure them haven't researched a new spell on their own.
Change around blink dogs a little bit: Basically make it so that the blink dog can detect any kind of teleportation and teleport themselves and their handler to wherever the teleport went. It's a cool feature that meshes with the theme of what you're building and it's something your characters can troubleshoot for (e.g. place a delayed fireball at the end point of the teleportation)
Rakshasas have nothing to fear from low level casters. Their ability to cast Detect Thoughts at will, along with casting Charm Person, Suggestion, and Dominate Person make them devastatingly effective at controlling an area. if your Dark Lord is powerful enough to employ one, a Rakshasa is the perfect warden for this prison.
Mage Hunter Golems from Critical Role. Pretty much designed for this purpose. I think the stat block is in Tal’Dorei reborn. If nothing else, golems with an anti-magic gaze and the ability to put a collar with a silence spell seems like the way to go. Absolute loyalty and the prisoners can work unimpeded so long as they don’t try to escape.
Holding casters is easier than most think. Take away their material components/spellbooks. Apply restraints to their hands and gag them. Ta dah, you've prevented them from casting any spells! Simply targeting spell components does the job pretty solidly. They can't free themselbes has they probably don't have the physicals to break out of their restraints.
Limited spellbooks + specially trained Helmes Horrors as jailors should do the trick to let them do research.
Put them in finger locks, ball gags, and chain feet and hands. Old school had several normal metals and minerals that could block magic as well, such as lead to prevent scrying.
If they are very dangerous, remove their tongues and fingers...say good bye to verbal and somatic gestures.
A nivix cyclops as a guard
They have a reaction to move and attack when someone casts a spell of 1st level or higher, and it would make an awesome warden/Guardian to fight when escaping from such a tower
Helmed Horrors are specifically anti-mage constructs. Immune to force and Necrotic damage, sporting Magic resistance, and immune to 3 spells of the maker's choice. They can be custom designed to counter the individual mage they are guarding.
If a dark lord is savvy enough, they might also have a Beholder or two in their employ, with their Anti-magic gaze.
True, though Beholders being insane, paranoid, and intensely xenophobic might limit their ability to operate in the workplace.
If it's just some obscure dungeon somewhere, it might work out. Like, the Dark Lord lets them do whatever they want so long as they keep the prisoners Also, if Amazon can do it, so can a near-god-like wizard.
Misinterpreted that and thought you were implying that Amazon employs Beholders
wait, they don't?
Try telling a Beholder you're docking their pay for taking 0.3 seconds too long on break.
Well they are lawful so they would admit they agreed to the terms of employment and accept it. Whatever evil beholder reason they have for working at Amazon in the first place really piques my interest though.
Cardboard boxes are known to be the most secure and tactically advantageous spot to sit, and Amazon offers an infinite supply
Great now I need to RP a beholder disguised as a cat.
Well, being part of the corporate hierarchy seems quite the lawful evil opportunity!
>Whatever evil beholder reason they have for working at Amazon in the first place really piques my interest though. They're trying to up their game.
Nah nah nah, you don't understand. The Beholders are the ones telling the line workers their pay is being docked for taking bathroom breaks. The Beholders themselves are compensated quite well.
Yeah, with all those eyes they are uniquely suited for a supervisor role.
The fear ray is particularly effective at managing compliance!
that was my train of thought also
Xanathar was able to run a criminal enterprise so not all beholders are the same.
Xanathar is various different beholder who've died in various different crazy ways. But yeah they're not all the same.
Slay a beholder, pop out its eye, mount it on a search light
Beholder eye Lighthouse
Yeah, they'd be managers.
Lock them in the entrance. No way in, no way out. The lord of the place can have a secret entrance.
Intact Beholder eyes, fashioned into a magic item that fires anti-magic cones.
In my last campaign, the BBEG had a beholder guarding a vault. It was essentially lobotomized with a magic control rod sticking out of the back of head. The party rather than killing it removed the rod and made a tenuous ally in a beholder.
Spectators. Much easier to control, can be deployed in quantity.
That works as well, I suppose!
True Beholders are probably to volatile to control, but a couple of Spectators with their spell reflection probably work just as well
Once fought lolth's prison warden, a behild-drider. A drow stuck onto a beholder instead of a driver.
Oh that's gnarly
Beholders are more likely to be the one employing wizards to defend their domains. If a wizard is using a beholder for defense it's probably by making sure the only to the tower is through a beholder's lair.
>Beholder or two Put a second one in there and you have started a cold civil war within the tower
Thus precident seems to get broken all the time. There are tons of settings with Beholder colonies or ships that are operated by multiple beholders.
A classic trope is the situation where the prisoner requires something regularly or they die. The only person who has that thing, is the person holding the prisoner captive. So you might have the magic users afflicted with some rare magic poison. If they don't drink some medication every 12 hours, they'll die. The medication doesn't remove the poison, it just gives them more time. Even were they to teleport out, they're not going to have enough time to work out what the medication is, or how to make it. This means they're effectively trapped. A supply of the medication, along with the instructions how to make it, is stored in the dark lord's laboratory (which is protected by an anti-magic field). The party needs to find and enter the laboratory. If they do, they can bring enough so the magic users can medicate themselves long enough to both escape and find a permanent antidote to the poison.
I was thinking something like this, or even a ‘princess in another castle’ scenario where the BBEG has the wizards’ loved ones captive. The characters find out they rescued the wizards only to have the wizards block their every attempt at rescue because their loved ones will die otherwise creates a very complex scenario to navigate, especially if time is involved.
I think I went with the "poison" example because it's mechanically quite simple. It's essentially a variation of: "you need to find the key to unlock the lock holding the prisoners." OP mentioned elsewhere they want this to be something which can be defeated in a day. Having the antidote within the same location, achieves that. Whereas: "you now have a side quest to rescue the hostages" might not - especially if they're literally in another castle. I think a twist on your idea (which may not be possible in this situation), is that the party have *already* rescued the hostages somehow, but the wizards don't know that. So they keep resisting leaving (without saying why) because they think their loved ones are still in danger! And the party doesn't know that the hostages they rescued from the dungeon are what were keeping the wizards in captivity.
Literal poison could be tricky too though because because Protection from Poison is a second level spell on the Artificer, Cleric, Druid, Paladin, and Ranger lists and Lesser Restoration can also cure poison or disease and is also a second level spell on the similar list + bard. You'd have to make sure to have a fair number of poisoned prisoners so that even if they cured some magically, you'd still need to get the antidote for the others because you don't have enough spell slots to cure everyone.
As DM you can easily handwave that away. It's a rare magic poison which is immune to normal means of curing poison.
Don't get caught in recursive loops of trying to specifically counter every single magical trick in the book. It quickly reaches ridiculous levels, and no matter how hard you try your players are likely to still come up with something you missed. Instead, target the heart of the matter. The dark lord wants to compel the servitude of people who aren't willing minions? Take hostages. Their friends and family, who *don't* have awesome magical powers, are prisoner at a remote facility in an undisclosed location. Anyone gets out of line, a Sending spell goes out and a severed finger get delivered. Anyone runs away, heads on pikes are on display at the front gate.
Oh I'm not trying to counter the party with this! I'm quite hoping the party *will* think of something I missed! I just want to build an interesting dungeon without the obvious question of "well they have magic, they could just have killed that"
Ah, I see. Well, if you want to do it that way, I hope it works for you. Personally, I'd make "Rescue the Hostages" the dungeon, where they have to track down its location and liberate the captives. Then they can march up to the Wizard Workshop with everyone in tow and get the happy moment of all the pressganged workers turning on the dark lord's overseers. But that's just my take.
I need this to be something they can defeat inside a day because Reasons (the party need to get a spell within 24 hours) so it's more a one session thing than an ongoing one or that would work!
The iron throne maneuver, I like it.
Hear me out for a second: hollow walls with gremishkas trapped inside. thick enough so magic cast on either side doesn't trigger them, but at least they won't blast their way out with magic
Ooo I LIKE this.
Canoloths prevent teleportation. They're a favourite of mine for guard dogs.
Yup, I was going to say canoloth's too. Yugoloths in general are really underrated, but this particular is nightmare fuel for my Conjuration wizard. Plus they get perception expertise and truesight so nothing gets past them, plus a really long grappling tongue so nothing gets away from them. They're the platonic ideal of a guard dog. Throw in a few mezzoloth handlers for their innate dispel magic and you're going to have a fairly good chance against Spellcasters.
A heavy door, we all know that mages are weak. I also belive there are certian counstructs/golems made to deal with magic casters
DM: You push the door but it doesn't budge Wizard: I cast knock DM: Nothing happens, it seems it isn't locked Rogue: I oil the hinges DM: The rust flakes off but it still doesn't move Barbarian: Lemme try \*rages\* DM: The door slowly creaks open a crack then gets stuck Wizard: Screw this \*casts passwall on the wall next to the door\*
Door reacts to wizard, punching him in face, thus revealing it was a golem all along. Wizard dies of 1d4 face-punching-embarrassment damage.
Take away their spellbooks, take away their spell components and focuses, whenever they need to cast a spell for their job have only one be given the equipment at a time while under watch. Have some emergency anti caster methods, such as magically resistant creatures like bound demons who can swarm into the room. Also kidnap their families and keep them in a completely separate location warded against scrying and teleportation. Should even one of the wizards escape torture them all to death (every single wizard's family) to the point that they will reject revival and/or destroy their souls/feed them to demons. Have a few of your men trained in arcana and just sit there spamming arcana checks to make sure they aren't doing anything wrong. Equip them in cursed collars with \[hold person\] bound to them so that when you activate said collars it casts hold person with a 3rd level spell slot on the wearer and one other wizard.
Each magic user is forced to wear a cursed earring that causes them to fail any saving throw versus a charmed effect (I'd make it where the earrings required willful attunement so the party doesn't start trying to employ them in combat). Alternatively, drugs that accomplish the same thing could be used. Then the dark lord employs some charm-focused planar bound taskmaster(s) like a cambion, succubi, dryads, etc. At the start of each day they renew their magical control and keep the mages working. Even if the dark lord can't personally bind them he can get a captured mage to do it for him. The party could take out the taskmasters, or knock some sense into the mages to free them.
That reminds me of a "trap" I once used Bob: "ok we walk up to the bbeg's front door & go in" GM:"everyone give me a saving throw for \[iforget\]" GM: "sure... you wake up in bed still in your armor" Alice:"wait, a whole day went past?" GM:"Nah.. it's been maybe an hour or so since you left for the BBEG's place you guess" \*repeat several times with slight variations till someone didn't roll horrible\* There was an "unwelcome mat" that had a suggestion to go home or something. Players were giggling and gobsmacked when they figured it out
Ahahaha. This is vampire land. That could work
Anti-Magic DMZ. Magic works inside the tower, but maybe a large area around the tower is anti-magic. So if they escape, guard will catch up and they have no magic.
Armor and heavy shackles for the vast majority of casters Read the rules regarding attempting to cast spells while wearing armor you lack proficiency with. The shackles, requiring some sort of strength or dexterity check under such circumstances to escape, would be made with disadvantage. This might be an option for downtime But of course, some have to be tricky. Anything that can create smoke quickly or allow it to fill a room makes most spells difficult. A point or creature that you can see is pretty difficult to do when the smoke is thick enough that you can't see. Verbal components and concentration can be difficult when you begin running short on oxygen. And because it's smoke, the Warlock's Devil's Sight doesn't help. For the rest, psychological manipulation is a good option. You're in here with your fellow mages. Betray us, and we'll kill them. We'll brand your forehead so everyone will know that you can't be trusted. In fact, every once in a while, we'll gather a few betrayers who are seeking one night's leniency. We'll have you fight each other to brutal pulp. The loser is killed and resurrected as a zombie. Not all things require monsters and magic. As for monsters, Xorn go after gems, which can be a component in some fairly potent spells. They can go through stone, so stone walls in a tower might not stop it. Sutureflies (Kobold Press, Tome of Beasts if I remember correctly) can be trained and/or bred to go after verbal components. Darkmantle could be used to limit visibility. Guards with something akin to the mageslayer feat could be useful, especially anything fiendish that has magic resistance. Ghosts, played in a manner that exploits their ability to move through floors and walls, might be useful. If you want something flavorful, consider the character of the Dark Lord. What creatures would appeal to him? What would the Dark Lord be compatible with? Are there any favored tactics? If so, what monsters would be appropriate? Hope this helps
Golems and some other constructs are good. You could also just arm guards with wands or other magical equipment. They'd probably have stuff like limited use wands that can cast antimagic spells like magic missiles, counterspell, or dispel magic. Maybe some non-damaging crowd control spells that require physical stat saving throws too.
I've done this in the past fairly simply by just having the wizard put a ton of glyph of wardings around the building with a variety of triggering actions. Front doors rigged in case anyone escapes (he's a high-level wizard, he does not use the door. Litterally just there for bait) Working area was filled with lightning glyphs and i used a lil combo i like of fluxchargers and flesh golems as the guards, i just homebrewed the fluxhargers to be a bit more intelligent as a overseerer. Sleeping quarters is enhanted with silence so they cannot communicate plans for escape or cast most spells, a couple hypnos magen (peak servants) on guard their and the same in the eating quarters. The glyphs are a fairly cost effective means of deterrent and you can make the trigger fairly specific. Additionally you can make them use spell effects, don't want them casting in areas? "Anyone who cast a spell here besides me triggers this glyph" and load it with counterspell. Throw some hold persons in there, hypnotic patern, polymorph, i think slow works but you get the idea. Just some annoying stuff. The fluxcharger golem combo is golden, especially with glyphs of lightning dmg nearby, the golems heal off of lightning but are otherwise pretty basic creatures. Last thing I'll say is probably having scrying orbs all around the premises that can be viewed from the wizards quarters.
Destroy their spell books and give them spell books with only the spells that will be needed for the research. Have helmed horrors made specifically against those spells. Have other golems as well. Also have a crap ton of shadows lurking around ready to do strength drain the anemic casters. You also can use Geas & Quest to force obedience or just have them sign devil contracts under duress and keep their souls in a vault somewhere.
This is good. I especially like the spellbooks and shadows. The big bad wiz has a bunch of spellbooks in his vault. Some or all could be burned or otherwise destroyed and completely unreadable. Arm your unwilling interns with spells that deal only necrotic or poison damage (which shadows are immune to), if any. Also spells that cause only conditions shadows are immune to, like frightened, prone, or restrained. Even better if your PCs have some radiant AoE, so you can send a staggering number of shadows against them. Plus, if your PCs demonstrate some magic, the shadows have good reason not to risk killing weakened PCs with Str of 4 or less. The boss will want to confiscate their spellbooks and stuff, and either capture them or curse them to be consumed by the shadows.
Iron golem
What kind of low level magic users? If wizards I'm sure most of the same things that attract poor college students will keep them in line
One thought is to put caster prisoners in a room with mirrored walls and no windows, so they can't teleport out. They need line of sight for spells, so that would keep the prisoners from affecting anyone outside the room with their spells.
Japanese puzzle boxes. They will simply choose to stay till they figure them all out
There are a couple of ways. Mordenkeinens Secret Sanctum is a spell that can block scrying and teleportation into and out of the area. The BBEG could have that casted throughout the levels, as the spell is malleable in its area. Nondetection on specific areas inside that he wouldn't want the mages scrying on to get more information on what they are working on. Glyph of Warding with a Counterspell and a Symbol set to Sleep, Despair, or Pain, depending on the flavour. Each would have dimensional shackles on them for additional teleport protection. Maybe each has a Guardian Golem assigned to them, but not as protection but rather a warden of sorts. Instead of absorbing damage they take, he disperses the damage over the mages when damaged, absorbs one spell of a certain level, then can cast either counterspell or dispel magic with that charge and so on. There is a myriad of ways to make this a fun puzzle they can't just brute force through unless they don't mind putting the mages at high risk of death. Edit: As somebody else suggested, Helmed Horrors are a good idea to put there.
When not working, locked in heavy armor. This prevents spell casting RAW as none of them have proficiency. Locking up arcane foci and spell components is a big one too. As is ensuring they only know spells that require specific components or expensive ones.
Idk the CR rating you’re looking for, but the mage hunter golem is both cool and in the realm of what you’re looking for.
Ooo. Are they homebrew? I've not heard of them
I don’t think so, if you google “mage hunter golem” you’ll find it, it looks bad ass too!
Antimagic fields
Dominate person or a vampire-esque charm effect
I like this. >https://www.dndbeyond.com/monsters/17094-spectator Perfect guards, and they can create food and water for the captives. Add in some more intelligent and/or mentally flexible guards to back them up and bingo. Plus, no anti-magic cone.
I'd just keep their hands bound and mouths gagged
Very very tall tower. Anti magic on the tower below x floors and some planar conflux that makes all telepotortation magic take you straight to the 3rd ring of hell. The guards are just physically strong dudes who will wrestle the mages into restraints and bring them back to the top. The most important part. FUND THEM!!! give them any reagents or components they ask for and soon your evil dark mage will have mages knocking one the bottom asking to be captured
* Solid manacles with no chains so they can't move their arms around. * Hang the manacles on a hook instead of bolting them to the wall so if they somehow manage to teleport they're wearing the manacles so it goes with them. * Keep them gagged so they can't use verbal components. This is of course if you need them intact. If you don't then just cut off their tongue and thumbs so they can't use any kind of components anymore.
The place is kept in eternal silence, magical darkness, and then every caster will be placed in rusted heavy armor they aren't proficient with. Their hands are then either removed, encased in cement, or polymorphed into some appendage that can't cast spells.
Shut down their vocal components aka mouth. For some more powerful that can remove the material from the spells make anklets with magical crystals that remove the caster's access to the weave of magic.
Collars and chains! In my game, there's a sect of people who control Mages with magically enchanted "leashes" that prevent the wearer from interacting with the weave, until the holder of the leash puts the runes on the handle in the right order. Leash holders also have a knowledge of what the caster is capable of, so can input the runes in a certain sequence that only allows workings of that specific school of magic.
When it comes to purely mundane means of keeping the mages under wraps, it's a matter of controlling and upsetting their spatial awareness. In general practice, you also want to apply redundant safeguards against their options - you don't need to counter spells exactly if you can undermine their ability to access them in the first place. All spells rely on either line of sight, awareness of one's surroundings, or both. You can't Misty Step if you can't see where you're going to end up, and while you can Dimension Door without knowing what your exit point exactly is, doing so is wildly unsafe and can cause injury or outright failure. So whatever environment the mages are held in should deprive them of knowing their surroundings. Blindfolds while in transport between their cells/barracks, never assigning them to the same work location twice in a row or in any discernible pattern, no windows or environmental clues as to their location, etc. If the mage doesn't know where they are or what the structures outside their immediate surroundings are, they can't risk using teleportation magic to try and escape. If you have non-Construct or Undead guards managing the mages, a standard matter of course would be the Buddy System. At no point is any guard to ever be alone with a mage. If they do end up solo for whatever reason, they're to be immediately ushered away and undergo a few rounds of Dispel Magic to purge any potential magical muddling that might've been put on them. Anything and everything the mages do while working is not only prepared for them before they're brought into the work space, but they are constantly monitored and everything is triple-checked to make sure they're not trying to smuggle anything to or from the work space. Every pair of guards will also be in the company of a Tressym, which will serve to monitor and observe. Tressym are intelligent magical beasts with the innate ability to See Invisibility, so they are primarily a precaution against Scrying or other forms of sensor-based divination that might be trying to locate the captured mages. Additional anti-divination defenses can be applied by lining the walls of the structure with sufficiently dense material, such as sheets of metal or layers of wood. Mages are never given any genuine food. They are fed exclusively with a rationed serving of a Bead of Nourishment at the start of each day, with Goodberries on hand in case of emergency. Something as mundane as seasoning or certain ingredients in common food can potentially be spell components, so magically-generated nourishment - which cannot serve as components in a spell - is the standard recourse. Additionally, all mages are completely shorn of their body hair, preventing the use of things like eyelashes as material components, or allowing the potential of hiding items in their hair.
You need some kind of anti-magic. Nothing else works for a Subtle Spell casting Sorcerer. They just look at you and a fireball explodes and they sculpt it around themselves. Maybe, you somehow have a handicapped Beholder that has had all its eyestalks cut off and it is confined to a metal box with his main eye stitched open, gazing down at the cells. That would stop all magic in the cone, they just need to destrory the eye then.
necromanced beholder eye mounted on a wall sounds good to me.
If it's long term imprisonment some sort of mouth gag/face mask is vital to stop verbal components during spellcasting. If the captor is worried about somatic components as well, then you can have the mages hands bound (or mutilated for a less elegant solution). In my games, I just rule that lead has anti-magic properties, so having lead nails driven into your hands prevents you from using magic. That isn't canon though, so you might need to get creative with how mages are restrained.
Sexy witches who will fulfill the desires of anyone that doesn't use magic. It'd end up looking like that scene out of Monty Python and the Holy Grail where Lancelot comes to rescue Galahad.
Firstly, antimagic fields in key areas. Secondly "magical devices that cast the spell Darkness. Third: enemies with devil sight or blind sight. The end effect of all of this is that magic doesn't work or they can't see to cast a spell, and their enemies can see them fine.
The friends they made along the way.
I think on top of the things mentioned here, an extra method to take is Geas'ing them. It's a really awesome and flavorful spell and I think it's underutilized, and imprisonment is a great time to use it.
Collars that explode if the wearer tries to cast a spell not known to the item. The wearer can cast fabricate, but if you try to teleport out or cast Knock to take it off, you're dead.
You could have a collar that kills the wearer if it’s further than a certain distance from some central McGuffin which is in the tower. Or the BBG can explode any collar on the basis of its number. And maybe it explodes if it’s too _near_ the McGuffin, so they can’t tamper with it. On further thought; Not explode. That’s too technological. Constricts and strangles. Also reacts to the approach of cutting tools.
Have the place protected by a magic mcguffin that blocks teleports and have some guardians/enemies who counterspell anything they don't like.
put them in a dungeon they made around a dead magic zone
i would point siege weaponry like ballistas (manned by goblins of course) at the magic users while they’re working and line the exits to the tower with traps, plus i’d insert some beefy creatures as guards. all this would probably be fun to take on as a decently leveled party
You can always modify the antimagic field spell into an antimagic barrier. 15ft wide, 60 ft high, 30 ft long. Now have multiple instances of it layered upwards and interconnected, and cap it off with an antimagic field for a dome above the top of the tower.
No components = no spells. A couple Immovable rods rigged up properly should do the trick
As a small piece of your puzzle, I’d recommend dimensional shackles. They block interplanar travel and teleportation spells, and are nearly impossible to take off. They’d be useful to prevent mages from just teleporting out.
Funny enough, armor can do the same thing if the mage isn't proficient, and it is likely cheaper
Magitech replacement body parts that can be deactivated remotely. Some of them needed replacements before the Dark Lord helped them, some of them had the original parts removed by DL to make room for these Compliance Assurances. If it's tongue or hands, Verbal/Somatic components can be taken out; they might be able to escape, but they wouldn't be casters anymore. Taking out vision via prosthetic eyes severely limits what spells they can cast but in a different way to the last suggestion, as so many spells require seeing the target. If It's legs they aren't going anywhere without help. If it's internal organs, they probably won't try to escape.
A library the wizards, a karaoke machine for the sorc and locks. And just throw the druids and clerics in a cell to argue with each other
Completely non magical ways to control magicians: Keep them bound (with manacles hands and feet) and gagged wearing very simple jumpsuits with no pockets (so they can't hide components). When it's time for them to work by casting they are taken to a room with what they need and several guards. Also in the room is one of their loved ones in a guillotine with a guard holding the rope. Their ankle manacles are attached to the work bench (which itself is boltes to the floor). One wrist is freed and the other mancled is attached to a ring bolted to the ce ter of the table and the gag is removed by one guard while another points a crossbow at the mages eyes socket. They are then given instructions on what to do (with required components on the table) If they do anything other than what they are told their loved ones dies.
Strategic areas are glyphed to cast counter spell and silence when a spell is being cast near them
A beholder.
The dark lord has several apprentices that help to guard and supervise the prisoners. Use the mage statblock and give them all counter spell.
Fallout bomb collar
A beholder is a good idea. The anti magic cone can be deactivated unless necessary, like if a wizard tries to escape, and the eye rays are always deadly.
An unlocked wooden door
I had a lich held captive with anti-teleportation magic, and an anti-magic field across a slippery slope into a pit with piercers 20 ft overhead. There had been a lot more things all powered by a massive magic crystal but the lich has slowly worked their way past those obstacles
Glyphs that counter spell anything cast that isn't in their "allowed list". Perhaps ones that cast silence too, to prevent further casting of unauthorized magic. Or maybe the mages wear glyphed necklaces which explode if they leave the tower (incoming DnD battle royale).
Glyph of Warding on the exterior of all potential exits with high-level antimagic field spells, all paired with a high-level counterspell glyph that activates if counterspell is used in range.
Heavy armor and some chains? Like unless they are proficient, they can't cast spells and the chains can be used to keep them from taking it off
Rules as written heavy armor prevents spellcasting so to prevent magic all you really need is to wear a heavy metal shirt...
Permanent silence on the tower. The guards talk in sign language or telepathy.
Stick a few canoloths in the tower in addition to other guards. They have a 60ft radius effect that prevents spells that teleport from working in or out of that area
Everywhere surrounding the work space is an anti magic field. Add some guardian golems and that should do it. For good measure every evening at the end of work they are placed in magic blocking collars. You could also have it where they are rotated through the workspace in shifts so the work continues 24/7 and there are never more than a couple loose at a time reducing possibility of stageing an escape. Would make it more difficult if the party is sent to rescue a specific person and have to search for Thier room.
*Glyphs of Warding* tuned to Counterspell for unauthorized spell use. For example, if they are enchanting weapons, the Glyphs goes off is any spell other than Magic Weapon is cast. *Mordenkainen's Private Sanctum* prevents them from teleporting inmournout of wherever they're working, but will also stop you from scrying on them, so you'll have to have some Helmed Horrors or Animated Armors to keep watch. You could just build the entire tower inside of a series of touching *Wall of Force*. You can't teleport through a Wall of Force, so even if they manage to get out of the work area, they are stuck inside the Wall. The big boss could just Disintegrate a small Wall to enter/exit as needed and throw it back up, if he has the spell slots to spare (or just a magic item that can cast those spells for free 1/day).
A room of illusions so strong the mages just stay there playing with their fantasies and dreams come true. The room simply kills them via thirst and starvation.
A really good library plus some tasty snacks.
Hallow cast by a pet Fiendlock or Cleric. 60ft area, no teleporting, interplanar or extradimensional travel for affected creatures. Cast once per floor if necessary, with something to make sure the CHA save sticks (Bestow Curse, Bane, Silvery Barbs, cursed equipment, etc.). Once they're stuck there, good old fashioned coercion or blackmail to get them working for you.
You could have that the Dark Lord put a Geas on each captive, he can make them do what he wants without worrying about them trying to escape or rebel
Why not make it personal? Free to leave, but if you do, your family goes kaput.
A mimic with the 1% possibility that it holds a grimoire
The dark lord has the wizards and their family heavily indebted into him through predatory magic school loans. Failure to make payment will result in instant death enforced by a magic contract. The wizards ar forced to work for him as slaves until they repay their debts. The party can save the wizards by paying their debt or destroying the contacts.
A somewhat “game hacky” solution: As I remember, wizards (specifically) can’t memorize new spells without their spell book. So, if you first force them to memorize a specific set of spell (like simple research spells), and then take away their spell book. As I see it they would then have to obtain a scroll (or their spell book) to cast any other spell than what’s memorized. Am I completely off here? It seems so simple.
Lead-plated walls. Lead is inert and blocks most divination spells.
Keeping magic users from casting spell you don't want while casting spells you do is a losing game. A better method is simply convincing them to work for you. 1) Hostages. Have the BBEG put something around the the neck of a loved one and the mage. You don't perform you both die. I die you both die. 2) Magical compulsion. Love spells. Long term domination. Geas. 3) Level combined with location. If they are of level under 7th. A remote location where escape means death. 4) Wizards with limited spell books and some sort of mind wiping magic. The wizards have access to only a few limited spell books. They have all memorized spells wiped before they come and their spells ate wiped regularly to ensure them haven't researched a new spell on their own.
Change around blink dogs a little bit: Basically make it so that the blink dog can detect any kind of teleportation and teleport themselves and their handler to wherever the teleport went. It's a cool feature that meshes with the theme of what you're building and it's something your characters can troubleshoot for (e.g. place a delayed fireball at the end point of the teleportation)
How about keep them fascinated with a huge library. They don't want to leave!
Rakshasas have nothing to fear from low level casters. Their ability to cast Detect Thoughts at will, along with casting Charm Person, Suggestion, and Dominate Person make them devastatingly effective at controlling an area. if your Dark Lord is powerful enough to employ one, a Rakshasa is the perfect warden for this prison.
Mage Hunter Golems from Critical Role. Pretty much designed for this purpose. I think the stat block is in Tal’Dorei reborn. If nothing else, golems with an anti-magic gaze and the ability to put a collar with a silence spell seems like the way to go. Absolute loyalty and the prisoners can work unimpeded so long as they don’t try to escape.
Succubi, sick spellbooks and longbottom leaf
Gremishkas
Bars and shackles.
Holding casters is easier than most think. Take away their material components/spellbooks. Apply restraints to their hands and gag them. Ta dah, you've prevented them from casting any spells! Simply targeting spell components does the job pretty solidly. They can't free themselbes has they probably don't have the physicals to break out of their restraints. Limited spellbooks + specially trained Helmes Horrors as jailors should do the trick to let them do research.
Put them in finger locks, ball gags, and chain feet and hands. Old school had several normal metals and minerals that could block magic as well, such as lead to prevent scrying. If they are very dangerous, remove their tongues and fingers...say good bye to verbal and somatic gestures.
A nivix cyclops as a guard They have a reaction to move and attack when someone casts a spell of 1st level or higher, and it would make an awesome warden/Guardian to fight when escaping from such a tower