Kangaxx Susceptibility to Mace of Disruption +2?

[Hanamichi]

I just finished Kangaxx recently (only one reload thanks to the trick about using the wizard eye as the focus of the demilich's imprisonment spells) but I'm confused because I thought Kangaxx could only be damaged by +4 weapons.

What happened was I ran Minsc up to the demilich dual wielding Crom Faeyr and the MoD +2 while the wizard eye received the brunt of the lich's spells. After 2 lower magic resistance spells and a whopping 13 damage from Minsc, Kangaxx just keeled over and died. I got several messages - critical hit, target immune to damage, target save vs death - which I assumed were successful blows from the mace. I went a mere three rounds before Kangaxx failed a save, curled up and died.

[Thomas]

Yeppers. You found the right weapon and tactic for that encounter sure enough.

The mace is considered to be heavier enchanted that +2 so it can hit all creatures in the game.

[Drakron Du´Dark]

The weapon destroys undead if they fail a saving , he is a demilich so he failed a save and died.
Note that because the weapon is only +2 it never did any damage to him on hitting, only after he fail a save he died.