Favored Power Attack( Complete Warrior, p. 98)
You are able to deal more damage against your favored enemies.
Power Attack (PH) , base attack bonus +4, Favored enemy ability,
When you use the Power Attack feat against a favored enemy, you may subtract a number from your melee attack rolls and add twice that number to your melee damage rolls. If you attack with a weapon in two hands, add three times the number. The normal restrictions of the Power Attack feat apply.