Ok , i m near the end .. but can't beat Cerdie .
She had some sort of spell who sometimes Oneshot any of my teammate if it's not me ..
Can' t find out wich resist i need or what damage type is this ?
Any clue would be welcome !
Thx.

I'm afraid I won't be able to help you much with this. She is a wicked beast and I was glad that I had been able to kill her. I know that she causes Confusion and Paralysis, as well the Speed Penalty. So maybe some items of Confusion and Paralysis Immunity could come in handy...

I am not sure either what it is that she makes all your companions die. Crappy thing is it persists even after she is dead and you have to visit a healer. 2 ways to defeat her:
1)If you are a caster cast crucifixion on her
2)Mass summon genies from magical boxes and have them attack her. An army of 20 genies made all final fights a breeze

The Purge spell, at level 12, counters her instant death-status ailment.

I've just met this problem with Diabolus. You should visit a priest and give him some money to heal you. Or just summon 2-3 Genies. The most ridiculous thing was when I tried to replay the battle, killed her... and MY PALADIN has immediately died after the victory *facepalm

BTW, if I have only level 6 of Purge, can it help?