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

Defensive Dismissal

FEAT 12

Activity reaction

Trigger A creature you're aware of critically succeeds on a Strike against you.

Requirements You're under a polymorph effect that you can Dismiss.

You change your form as a means of evading a potentially fatal blow. You Dismiss the polymorph effect you're under, and the result of the triggering Strike becomes a success instead of a critical success. If you would no longer fit in your space as a result of returning to your normal form, this action fails and you don't Dismiss the polymorph effect.

Pathfinder Howl of the WildORC