pf2e.fyi
From Pathfinder Impossible Magic, which isn't enabled.

Final Spite

FEAT 8
NECROMANCEROCCULTPOISON
Activity free action
Frequency once per 10 minutes
Trigger A creature reduces you or a living ally within 30 feet to 0 Hit Points.

You can trigger this action even while Dying. You can channel the power of death into a poisonous spite. The triggering creature takes 4d4 persistent poison damage with a basic Fortitude save against your spell DC. If the creature kills you or your ally as part of the trigger, the creature gets a result one degree of success worse than it rolls on this save.

Pathfinder Impossible MagicORC