Tactics against Necromancers.

...to instantly destroy 1000 skeletons with an explosion, you need a magic power of 76!...

A small mistake. A level 24 Sorceress (to guarantee all skills are expert) with the Sphere of Ill and Titan's Armor, having a magic power of 26 without these artifacts (and with other artifacts, this is quite possible), will destroy these skeletons with a single blow.