Merciful Palm (Martial Arts Maneuver)
From D&D Wiki
The palm that holds back is often more powerful than the fist.
Level: Soft 1
Type: Action (Attack)
Description: As part of this maneuver, you make a single attack with your unarmed strike. This attack is nonlethal, but deals double damage. For every iterative attack your base attack bonus gives you, the damage of the merciful palm increases; its damage is triple your unarmed strike damage at BAB +6, quadruple at BAB +11, and maxes out at five-fold at BAB +16.