Unless you're willing to waste a PfM scroll to defeat Kangaxx the Demi-Lich, you have to take him out with Edwin, since, I assume, he's the only one in your party who can cast Spell Immunity. With SI: Abjuration and Death Ward on, he's completely invulnerable to Kangaxx. As Olorin said, MMM is the best weapon against him, at least with Edwin, and THAC0 will cease to be a problem if you buff him up with stuff like a Potion of Power, Potions of Mind Focusing (increases DEX, which increases Missile THAC0 modifier), Aid, and Champions Strength.
Of course, the best answer to your question is this link
Dundees Tips to Slaying Kangaxx
[ 03-07-2004, 08:09 AM: Message edited by: Rataxes ]