Needs review
Source: Dragon Magazine #339

Description: Your blows have the possibility of stunning your opponents.

Prerequisites: Favored Enemy (any humanoid)

Whenever you successfully score a critical hit against a humanoid creature humanoid (of a subtype you have selected as a favored enemy), the humanoid is stunned for 1 round unless he succeeds at a Fortitude save (DC 15 + your favored enemy bonus against that creature).