No clue how to finish this one, it's like at 0 hp for 5 min

https://imgshare.io/image/broken.pGp2OK

Drain DEX to 0.

Also - obviously - it has abysmal Reflex saves. Meaning Grease, Web and all such things will work.

i mean it's dead it has 0 hp, it just won't die and it's not a troll

1. You did not put the part of the card where it is said about regeneration.
2. The ability Coup de Grâce serves this exactly purpose. If it has 0 hp then just coup de grâce it with all the characters, and sooner or later someone will pass the saving throw.
3. Alternatively, learn what prevents its regeneration and use that.

Forgot about cup de grace, thanx

For me it has +33 reflex

It shows: Regeneration 10 (negativ energy)

Any "Inflict" spell should overcome the regeneration.

the card actually showed regeneration (positive) to me. weird.

It is actually laughably easy to kill him once he is down at 0 hp. Ember (if you use her default build) will learn healing hexes. He is a undead, and his regeneration is overcome by doing positive damage. The reason these hexes matter, is unlike using a traditional spell or say a aoe channeling, he gets no spell resist versus the hex.

So Ember can just walk up, do the healing hex to him on the ground, and as long as she hits his prone touch ac (which is not very high, I know it is less than 20) hes dead no save, no spell resist.

Coup de grace is garbage in this game. Late game enemies you would use it for have save bonuses so high they need to roll like 5 or lower or they make the save and it does nothing. Playful Darkness for example saves coup de grace on normal difficulty with something like a d20 roll of 3.

Nice way to kill them you found there!

Coup de grace save DC scales with damage. The save height for the Fortitude save is 10 plus damage dealt. Since a coup de grace is an automatic critical it is adviced to coup de grace with a weapon that has a good critical multiplier combined with a good base damage (and of course a character that has a good stat to add to the weapon's damage).

A dwarven waraxe (1D10 x3) will making coup de grace easier versus those done with a dagger (1D4 x2).