[Kaleban]

Here's a much easier way:

Have 1 fighter-type character purchase a Protection from Magic and Protection from Undead scrolls.

Huddle your party in NE corner of the tomb area.

Have the Fighter (make sure he has a +4 or better weapon (Flame Tongue, Mace of Disruption, or Staff of Rynn are able to be acquired early on...) move to open the tomb.

As soon as Kangaxx the LICH pops out and goes through his dialogue and turns hostile, cast the PfM scroll on him! This will make all of his spells and abilities fail. Lure him over to the SW corner of the tomb, and proceed to pound him.

When he turns into the demilich and goes through his bit of dialogue, use the PfU scroll on your same fighter. He can now pound with impunity, and Kangaxx won't go after the rest of your party as they are out of his sight radius. Eventually his morale will break and he'll start zipping around, I try to corral him back up the steps to his tomb, if you put your fighter in the middle of the catwalk, the demilich cannot pass.

I have NEVER lost a character to imprisonment using this method, and its just gravy for soloing.