As a reaction, which you use when you make an ability check using Constitution, Dexterity, or Strength or a Fortitude or Reflex saving throw, you can focus your mind to overcome your body’s limitations. Roll a d3 and add the result to the roll. You can do so after the roll but before any effects of the roll occur.
You can expend 2 additional stamina dice to roll 2d3.
You can expend 4 additional stamina dice to roll 3d3.