Ultimate Combat pg. 236
Locate Weakness
You roll damage twice when you roll damage for a critical hit and take the best damage.
Divination \ \
arcanist 3, bloodrager 3, hunter 2, inquisitor 3, magus 3, occultist 3, psychic 3, ranger 2, sorcerer 3, witch 3, wizard 3-level
Casting time: 1 standard action
Range: personal
Duration: 1 minute/level
Targets: You
Componenent: V, S, M/DF (a pickled predator’s eye)
Description
You can sense your foes’ weak points, granting you greater damage with critical hits. Whenever you score a critical hit, roll the attack’s damage dice (but not extra or precision damage dice) twice and take the highest result.