Staff of the Archmage
Unique Item, discussed in this topic on UBB
To charge it you either need to spend 8/9 turns and/or about 65,000 mana charging. Not sure yet if you get it just waiting those turns or you can acquire it with a positive income and not specifically charing. I have recharged it both ways. I'll try and remember to post later. But, it's difficult to make runs using it, as you will have to stop after each attack for at least some number of turns. It can be resisted like any other item. Battle sample below. Damage from Fire Elementalist is mixed in and not sure what was resisted but staff wasn't resisted or it would say so just like any item. Not sure if it has increased penetration. It does not TAKE mana from you on use, however.
(#xxxx) used Staff of the Archmage. Fire Elementalist casted "Arcfire". Fire Elementalist casted "Firestorm". (xxxx)'s 11900 Zombies are slain.
(via DukeRustfield May 26, 2008)