Superior Unarmed Strike (3.5e Feat)
From D&D Wiki
Superior Unarmed Strike [General, Fighter Bonus Feat]
A boost to the unarmed
Prerequisite: Str 18, Dex 18, Con 18, Power Attack, BAB +6
Benefit: When making an attack with an unarmed strike or natural weapon, multipy all damage done by 2.
Normal: You do not multiply your damage.