Overseer of the Damned Combos
Green Dragon + Overseer of the Damned + Pandemonium
Green Dragon + Overseer of the Damned + Terror of the Peaks
Green Dragon + Overseer of the Damned + Warstorm Surge
Horobi, Death's Wail + Shadow Alley Denizen + Overseer of the Damned
Combo result
Destroy any number of nontoken creatures opponents control whenever a black creature enters the battlefield under your control. Destroy any number of nontoken creatures whenever a creature dies.
Prerequisites
All permanents on the battlefield. You have a way to put a black creature onto the battlefield under your control.