pf2e.fyi
From Pathfinder Howl of the Wild, which isn't enabled.

Brutal Crush

FEAT 4
BARBARIANDRUIDMENTAL
Activity 1 action
Prerequisites animal instinct or untamed order
Requirements Your last action dealt bludgeoning damage using an unarmed Strike granted by a morph or polymorph effect.

You've learned how to cloud your foes' minds with the brutal impact of your repeated attacks. Make an unarmed Strike against the same target. If the Strike hits and deals bludgeoning damage, the target is Stupefied 2 for 1 round (Stupefied 3 on a critical hit).

Pathfinder Howl of the WildORC