Combat Stamina (Combat)Source Pathfinder Unchained pg. 112 (Amazon)
You stop at nothing to drive your attack home.
Prerequisites: Base attack bonus +1.
Benefit: You gain a stamina pool. After you make an attack roll with a manufactured weapon, unarmed strike, or natural weapon attack with which you are proficient, but before the results are revealed, you can spend up to 5 stamina points. If you do, you gain a competence bonus on the attack roll equal to the number of stamina points you spent. If you miss with the attack, the stamina points you spent are still lost.
Special: Since you have a stamina pool, you can spend your stamina points to use any combat tricks associated with combat feats you possess.