If you have a powerful mage with robe of vecna, cast timestop improved alarcity then spam his head off with spells, i managed 3 lower resistences,6 chain lightening, 2 abi-dalzeem and 3 fireballs and 2 magic missiles and one finger of death.
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In nomine Imperatis, guard our armour and our gaze; lubricate our projectile weapons that they do not jam. Bless and brighten the beams of our lasers; fiat lux in tenebris.
He is the Master of Mankind by the will of the gods and master of a million worlds by the might of his inexhaustible armies. He is a rotting carcass writhing invisibly with power from the Dark Age of Technology. He is the Carrion Lord of the Imperium to whom a thousand souls are sacrificed every day.