Prerequisite:  Knowledge (arcana) 5 ranks or Knowledge (nature) 5 ranks, ability to use any polymorph effect.

Benefit: A creature you deal damage to has difficulty using or maintaining polymorph effects until the end your next turn. To use a polymorph effect it must make a concentration check (DC 15 + twice the level of the effect). If you deal damage to an opponent under a polymorph effect, that opponent must succeed at a Will saving throw (DC 10 + 1/2 your character level + your Wisdom modifier) or be forced back to its original form. If you score a critical hit against such an opponent, no saving throw is allowed.