chromatic doom, help needed Options

[Kerkes]

I need some help with chromatc demon. My party is: riskbreaker lvl 21 - long sw +3 and equlizer
valygar lvl 19 - +3 club and +4 shortswrd
ber-cler 9-21 - foa+3, flail+3
ber-mag 9 -18 staff+3
imoen 19
cernd 17
I usually did this with more fighters and the fight was easy. But now I have only two, since my cleric must heal. Imoen seems not to be able to hurt him with adhws after firing 3xlower resistance trigger (she has vecna). Cernd, on the other hand, does wonders with his aura clensing and unleash energy. Isn't that the same kind of damage(magic)? why doesn't adhw work? I don't get any message about what's happening. Yet unleash energy does not seem to be enough (does 20-25dmg) , demon gets "near death" but that's as far as he'll get. As soon as Cernd is out of unleash (he has 6 or 7 I believe), I may as well reload. I've also tried magic missile under imp.alcatry (does nothing) , waiting for demon to switch to ice form so that flame arrows hurt him, but he killed my spellcasters before that etc. Any hints? In his red demon form, how can I hurt him with elements? I just hope it's not ice. I also don't get any message for bolt of glory.

[Shadan]

OK, sorry again. It seems I won't do any more suggestion on this forum since my memories sometimes misty what was in 4.2 and what in v5... However I am replying v5 now again with wild mage protagonist, just for fun. At least this immunity info was useful for me in my current game.