From Pathfinder War of Immortals, which isn't enabled.

Slay

FEAT 12

Activity 2 actions

Requirements Your target is Doomed 2 or greater.

You finish your target with a vicious attack. Make a Strike against the target. If you hit, the target takes 4d6 extra precision damage with a basic Fortitude save against your class DC. If the target critically fails, they die. This is an incapacitation effect. The creature then becomes temporarily immune to your Slay for 1 day.

Pathfinder War of ImmortalsORC