Mace of Variability

It is rather unreliable.

A great shimmering mace

(-4 to +16), (-4 to +16) great mace

Chaos brand

This weapon has no fixed damage or accuracy bonuses. Anything between -4/-4 and +16/+16 is possible. The mace has a 40% chance to change its attributes each turn it is wielded. Changes its color as well.

Desirability

Probably not very useful, since it is two-handed and requires a large investment in Maces & Flails skill, and in return gives you unreliable enchantments and the dangerous chaos brand.