Well, Jan proceeded to pickpocket him for the cheesy Ring of Gaxx. I had drunk a potion of haste and an invisibility potion as well as casting non-detection on him so I could bail him out after the job was done.
A horde of inconcequential summoning spells stood ready to soak up some instadeath. The next wave of summons was hardier including a nishruu, a Mordenkainen's Sword and a steady stream of skeleton warriors (yep I read your guides
).
I sent in my main character, a berserked babarian wielding Crom Fayer and Flame Tongue standing right behind the skeleton warriors.
My other party members kept themselves a bit away from the line of scrimmage.
My mages (three of them) was busy throwing a steady stream of counterspells while Mazzy Fentan was providing fire support (Gesen Bow). Anomen animater skeleton warriors (they called him Anomen the Animator afterwards [img]tongue.gif[/img] ).
At a point Kangaxx cast Meteor shower at which point I evacuated to the first floor. No obscene use of cheese (I was already quite guilty after having exploited the pickpocket bug) so I only used the breather to berserk my babarian and got down there again right after (evacuating a room after somebody casts Meteor Swarm seems a sensible move from a roleplaying point of view).
I proceeded with the same tactics which proved successful. Kangaxx the demi lich fell easily.
Kangaxx had summoned an efreeti that proceeded to kill Jan after the game went into freeze mode (Jan had snuck up to try backstabbing Kangaxx with the Cutthroat).
I played on core difficulty so I'm not especially hardcore.