Imp Overlord is an imp boss. At the lowest Threat it has 960 health, hits for 22 and carries 4 armor; the uber version you meet in the Mortal Arena has ×1.6 the health and ×1.75 the damage. You need Overlord's Horn to call it out.

It waits at the end of Demon Gate, and belongs to Adventure Mode.

Every kill rolls its list 5 times. 8 Uniques sit on it: four ordinary ones splitting 90.0% of it between them, and four Exceptional ones splitting the last 10.0%, which puts any one of those at about 1 in 40 of what it gives up. The Exceptional ones are The Open Door, The Hundred-Handed Court, Rifthunger and Doormaker.

It opens every fight with King's Chain, then fights with Rift Hunt and Brimstone Ring. The cast bar under its health names each big move as it winds up, so a party can call them out to each other. At 60% health it changes phase with Break the Gate into The Gate Breaks. After each big set piece it stops for a breath: that is the opening to punish. At 15% it makes its Last Stand with Gate of Ruin, one named, fully telegraphed finisher, and no burst of damage skips it. The uber version in the Mortal Arena fights in three phases (Gatekeeper, Gate Unbound and King of Ruin), grows between them, and adds Chain Gang and Void Eruption. Its weak spot: Break the Chain. Dash away while the chain drags you: it snaps and he stumbles.

It calls in Void Portal.