Send a summoned creature like a fire elemental to take the beating from the spells and have your fighter with the mace of disruption whack him. Also make sure you are protected from horror, and have the cloak of mirrors on. After reading how tough he was I was preparing for a long bloody fight but Minsc went up like this and just whacked him.
If Kangaxx fails his save hes a goner.
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Hail Aerie !
Ruby Gaurdian of ASLB