Needs review
Source: Book of Exalted Deeds

Description: Your mightiest attacks weaken evil foes.

Prerequisites: STR 13, Power Attack, Base Attack Bonus +8, Resounding Blow

Whenever you deal a critical hit to an evil creature using a melee weapon with which you are proficient, your opponent must succeed on a Fortitude save (DC 10 + 1/2 your character level-your Cha modifier) or take 1d4+1 points of temporary Strength damage. A monk's unarmed strike is considered a melee weapon for purposes of this feat.