I know it's not in line with the official TOEE campaign setting, but I think the endgame could be spiced up with some very difficult optional bosses. Hardcore type stuff. Just a thought.
I think the War of the Golden Skull covers that- it's only a guess since I never tried it myself but it leads to a final encounter with 4 avatars to fight, determined by your alignment...
Oh, really? Nice. I'm not that far yet. It just hit me that a lot of the encounters are too easy, even with 3 party members(Fighter/Rogue/Barbarian, Wizard/Fighter-1, Cleric/Fighter-1).
