I found it better to arcane explosion when someone got frozen. That way they are all doing damage to the frozen target plus the boss. If there are any skellys up they die fast too. I always arcane explosion the skellys when they spawn with my 3 mages. Oh and watch the uk video so you can see where to pull the boss. You keep your guys behind a wall at the entrance and pull the boss back with your pally. The video shows it pretty well.