The build focuses on maxing out the following skills:

One skill point is added to the following skills:

Rest of skill points go to the following skills:

Mercenary: Act II Nightmare Offensive Mercenary (Might Aura) with the following gear:

For the stat point distribution, see Summonmancer.

For this build, the summons are the tanks, the mercenary is the corpse-maker and you are the corpse-exploder. With Corpse Explosion as the main attack spell, the Ultimancer can arguably take down the largest crowds of enemies in the least amount of time in Hell difficulty. The strategy here is to use Attract on a monster, wait for the enemies to swarm in, cast Amplify Damage, watch a corpse drop and *bling* away. With 95% Crushing Blow on your mercenary who hits at a 6-frame rate, any monster, or boss, will succumb very quickly. To kill bosses even faster, make an Iron Golem out of an item that has the Crushing Blow bonus.