The Drow Mages on Ooze have a set of buffs that they instant-cast that make them very hard to kill. These are often cast before you even enter the room (even invisibly.) The fact that their very next spell is always Acid Sheathe makes them practically speaking invulnerable to damage.
Either remove these spells from their scripts, or remove Acid Sheathe from their lists. These mobs are impossibly hard to deal with because they ignore CC, instant-cast all their survival spells, and then cast damaging spell after spell after spell at your party.
These very often come in threes in the quest. It's beyond frustrating.