It's a pretty challenging fight with all mana DPS to begin with. If you have the means, your best bet is to stack stamina and mp5(spirit for the mages, I suppose.). Unless you can get to the point where you kill him after the first incite, he will run you out of mana with chain casting armour, holy nova, blizzard, etc. If your characters are a little more resilient, and have some regen, you might be able to do it.