serialies: I Aint getting any kind of dialogue option.
I think i might have broken this by attacking istwan the moment i saw him.
I assume he's probably meant to talk to you and that raises a flag/trigger, but if you attack him no dialogue = no flag.
If im wrong, and you just fight him until you get the "haha i never die" dialogue then ok, donno what im doing wrong.
But if im right, just a word of caution to everyone to dialogue first, fight second.
You have to fight him first and flee after he said that he is immortal (you have to defeat him first). If you manage to escape the dungeon alive you can go to the herbalist woman and ask her about his immortality. Then you have to fetch some holy water and return to the dungeon to defeat him once and forever. ;)