Was the BG 2 cumulative spell failure just for one round or for the whole fight? Did it stop the ability of some creatures to summon stuff? Did it also remove existing magic effects like 'Protection from magic weapons'? The BG 2 wizardslayer kit sounds very powerful for a fighter, the only downside is that he can't drink magic potions?
- every hit bestowed 10% spell failure chance onto the target, the duration was longer than 1 round much longer, so the effect most likely lasted thru the fight
- it doesn't stop spellcasting, just gives a chance for casting failure
- the attacks don't dispel anything (that would be a tad too powerful, right?) so proMW still works, he could use normal weapons then, for maximum protection from the attacks a wizard probably needs Pro Normal Weapons and ProMW
- he gets 2% SR per level
- he can't use ANY magic items (except weapons and armor), that means no potions, rings, amuletts, etc
All in all the worst of the fighter kits in BG2 imo. Of course (like in the Tactics mod) if you encounter wizard slayers who shoot arrows of dispelling, that's a pretty bad situation if you don't have ProMW up.