pf2e.fyi
From Pathfinder Lost Omens Shining Kingdoms, which isn't enabled.

Fiend Slayer

FEAT 16
ARCHETYPEDEATHVOID
Activity 1 action
Archetype Wylderheart
Prerequisites Wylderheart Dedication
Requirements Your last action was a successful Strike against a fiend that dealt damage.

Your attack tears through a fiend, possibly sending it back to where it came from. The fiend you just struck takes 80 void damage with a basic Fortitude save against your class DC or spell DC, whichever is higher. On a critical failure, the target is also Stunned 1. Regardless of the results of the saving throw, the target is then temporarily immune to Fiend Slayer for 24 hours.

Pathfinder Lost Omens Shining KingdomsORC