I heard from someone that the only way to get this helm 'legally' (not by cheating), is by defeating the Demonknight the first time it appears. Well, I bought Ike's tour, and in the middle of it, the Demonknight appeared and started slinging fireballs at Ike/tourists. I tried everything I could, but I simply couldn't kill the Demonknight. He resisted all my holding spells - all my spells which includes a saving throw, in fact. And I could only hit him when I scored a critical hit, which is SUPPOSED to automatically hit anyway.
Any ideas, anyone?

Today I´ve been trying to defeat him in a MP with using my best warrior in the 6 characters and... NOTHING . The best time I did it I hit him 4 times making him a damage of around 100 hp. Then I tried with a mage, casting emotion, hold monster, etc and...NOTHING . There should be a trick to hold him but if there is, I don´t know it.

I think the game makers made it impossible to defeat the Demonknight in this instance, since I faced the same scenario when I tried to kill the First Reader (is it Tethoril? The guy was the overall head at Candlekeep ) just to get the Staff of Force he was supposedly carrying - as described in the game manual. Unfortunately, spells with a saving throw just don't work on him; only criticals hit him (and I clocked 180++ damage on last count, before I finally got fed-up); exactly the same infuriating situation I face with this demonknight.
Nevermind, just wait until I reach the appropriate scene when I can FINALLY get to whack him... *nasty grin*