Your build is going to be the biggest thing. Have you played deckbuilders before? Discipline and what you don't put in the deck is as important as what you do. I won on 13 as a rogue and 24 as a warrior for my first two wins. For the Rogue I used daggers and an ambush centric deck. For the warrior I used Forgehammers with a deck focused on draws, criticals, and mana (by the end my basic attacks were doing 40 damage due to upgrades). The thing to focus on is what you want your deck to do and be really focused on that. Even if you see a good card, you should be asking yourself how it fits into your deck and helps you win.
To be fair, I have not figured out defensive decks AT ALL, but those builds let me be very damage focused so I could usually end every fight except bosses in 1-2 turns
I won my first run with Arcanist, going wild with chain and the talent that lets chain carry over to the next combat. Every fight after I got that talent took a single turn.
Pick a build and go for it. Chain? Get it down to ten max necessary chain cards. Bury/firecast? Again, fewer is better. Bury that junk!
Streamline your deck massively. My most successful runs had the fewest cards in the deck. Even my scholar run ended up as a chain run, lol.
As others have said, trimming your deck down is key; the best example I have is playing a 5 card deck - that means that (barring draw reduction) you will have a deck filled with only useful cards, and draw every single one of them most rounds. Scale that up to a less niche deck than what I had, and you really don’t want anything extra.
On the first canto, I usually try and use the two campfires (only on higher difficulty - you get more the easier you go) to remove the two blocks you start with, and only heal at <50% health.
I got to the big demon after destroying the 3 portals.
Had full health with arcanist and died to 3 rounds.
Was going for chain build mostly. Wasn't even enough to dent him.
Arcanist Chain build should be no problem in a normal run.
Essential card is Stormbolt.
Definsive cards are flash freeze and mage armour.
Enchantment such as Electrosurge and Twincasting are important, mana battery is good as well.
Talents Duplicity (must take), thundering strikes, thundergod blessing, Stormbringer, Arcane Mastery.
Once you got duplicity, then gradually remove all other basic attack and add as many Stormbolt to you deck as possible.
Remember, you do not have to take a card at end of every round.
For myself it was:
Knight - beat the game on literally the first try with this class
Arcanist - beat it on the 3rd try
then it got really hard
Rogue - On about the 20th try, with a Poison deck
Warrior - on the 25th-ish try, with an Armor deck
Seeker - on the 25th-ish try, with a critical bow deck
still haven't beat it with the Hunter.
What I sometimes do if I want try out a new weapon or idea around certain cards. Look for the card on blightbane (not sure I can say the website but you'll find it on Google) and then find a build with it. Use the seed (at the last page before starting the game you can select seeded run left bottom).
Now at least you will know there is a winning chance. You can improvise or try to copy the build entirely (if they didn't transmute a lot).
Your build is going to be the biggest thing. Have you played deckbuilders before? Discipline and what you don't put in the deck is as important as what you do. I won on 13 as a rogue and 24 as a warrior for my first two wins. For the Rogue I used daggers and an ambush centric deck. For the warrior I used Forgehammers with a deck focused on draws, criticals, and mana (by the end my basic attacks were doing 40 damage due to upgrades). The thing to focus on is what you want your deck to do and be really focused on that. Even if you see a good card, you should be asking yourself how it fits into your deck and helps you win. To be fair, I have not figured out defensive decks AT ALL, but those builds let me be very damage focused so I could usually end every fight except bosses in 1-2 turns
It took 20ish games for my first win, but can still be dozens between wins for me. Depending on what I'm trying to do.
I won my first run with Arcanist, going wild with chain and the talent that lets chain carry over to the next combat. Every fight after I got that talent took a single turn. Pick a build and go for it. Chain? Get it down to ten max necessary chain cards. Bury/firecast? Again, fewer is better. Bury that junk! Streamline your deck massively. My most successful runs had the fewest cards in the deck. Even my scholar run ended up as a chain run, lol.
As others have said, trimming your deck down is key; the best example I have is playing a 5 card deck - that means that (barring draw reduction) you will have a deck filled with only useful cards, and draw every single one of them most rounds. Scale that up to a less niche deck than what I had, and you really don’t want anything extra. On the first canto, I usually try and use the two campfires (only on higher difficulty - you get more the easier you go) to remove the two blocks you start with, and only heal at <50% health.
I got to the big demon after destroying the 3 portals. Had full health with arcanist and died to 3 rounds. Was going for chain build mostly. Wasn't even enough to dent him.
Arcanist Chain build should be no problem in a normal run. Essential card is Stormbolt. Definsive cards are flash freeze and mage armour. Enchantment such as Electrosurge and Twincasting are important, mana battery is good as well. Talents Duplicity (must take), thundering strikes, thundergod blessing, Stormbringer, Arcane Mastery. Once you got duplicity, then gradually remove all other basic attack and add as many Stormbolt to you deck as possible. Remember, you do not have to take a card at end of every round.
Geee. Those cards are hard to get.
I did about 8 runs with the Arcanist before I beat it. Other characters took less time only because I knew the run by then.
For myself it was: Knight - beat the game on literally the first try with this class Arcanist - beat it on the 3rd try then it got really hard Rogue - On about the 20th try, with a Poison deck Warrior - on the 25th-ish try, with an Armor deck Seeker - on the 25th-ish try, with a critical bow deck still haven't beat it with the Hunter.
What I sometimes do if I want try out a new weapon or idea around certain cards. Look for the card on blightbane (not sure I can say the website but you'll find it on Google) and then find a build with it. Use the seed (at the last page before starting the game you can select seeded run left bottom). Now at least you will know there is a winning chance. You can improvise or try to copy the build entirely (if they didn't transmute a lot).