pf2e.fyi
From Pathfinder Dark Archive (Remastered), which isn't enabled.

Cranial Detonation

FEAT 18
Activity free action

Frequency once per round
Trigger You successfully reduce one or more non-mindless enemies to 0 Hit Points with a spell.

As your overwhelming psyche fells a creature, you use its flickering consciousness to detonate psychic energy from the creature's head. Each enemy you reduced to 0 Hit Points dies and its head explodes. Each exploding head generates a shock wave in a 15-foot emanation around that enemy. Each creature in any of the emanations takes 10d6 bludgeoning damage with a basic Reflex. If this damage reduces an enemy to 0 Hit Points, its head also explodes, potentially damaging more creatures and potentially causing more detonations. A given creature can take damage only once from a single use of Cranial Detonation.

Pathfinder Dark Archive (Remastered)ORC