I got a small problem with that a**. No matter what I do I can't seem to kill him. I've tried to hit him with every spell I got and he's resistance to all my spells. Does anybody have any clues that could help me out? Thanks for all the help.

Are you talking about the Ice form of the Chromatic Demon or about the Ice Golems in the lower left room? If latter look around the level for notes from the deceased wizards. They will tell you how to kill the monsters in the Air, Poison, Fire and Ice room.

He never fully leaves the ice room for long, just use the crimson dart on him from floor 1 of the keep if you find him tough. Reading the library notes should make it obvious what else needs to be done.

the Firetooth crossbow from the group on the roof can help too.

SPOILER
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*he is invunerable*
You have to turn the fan on in the air room then open the door for the acid room clear that room out n open both doors to the acid room. Then switch the fan to high(make sure the door of the air room is open on the side closest to the acid room) and the acid will blow in to the ice room (if you have the ice room door open). Then the ice golem will become vunerable.