How did you handle it?
This was my party Paladin, F/T MC, R/C MC, F/D MC, C/M MC, Bard.
WARNING Spoilers below....
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So for me what made this hard was Belhifet casting dispel on the party removing all prebuffs, and the fact that all 5 enemies (2 iron golems, 2 cornagons, and Belhifet) were magic resistant. This meant I had to cast short cast time buffs ASAP and made offensive magic much less useful.
So my strategy was to take out the golems , then the cornagons, then Belhifet. Mainly because the minions were causing so much damage to my party members.
Buffs I could get off quickly before melee ensued were: haste (barely in time), prot from evil, defensive harmony.
The druid conjured elementals as distractors.
All enemies required magical weapons to defeat (+3 or better, I believe).
Holy might took to long to cast for the Paladin and R/C, so i never used them. Damage happened too fast (they were always disrupted), and the damage was too great.
The Bard sang Song of the Sith. But was also used as a distractor for Belhifet mid-battle. Casting spells on him caused him to retarget her, so she could then start singing again while he chased her in a circle around the fray.
The Paladin, F/T, and R/C engaged one golem at a time. Each would run away if badly damaged, with either the Druid or R/C healing them, and then returning.
Once the melee began, additional buffs were cast by the C/M: recitation, courage, hope, prot evil circle. And symbols of hopelessness and pain (which almost never worked). I did get lucky once with a chromatic orb holding a cornugon.
Once a few elementals were conjured, the F/D joined the fray.
A major annoyance were the traps in the floor: they dispelled buffs that needed to be recast, and disrupted healing spells.
So I'm curious, how did other people handle this? It seemed very hard for me.