Impossible Technique 
Feat 20
Source Pathfinder Core Rulebook
Trigger An enemy's attack hits you or you fail a saving throw against an enemy's ability.
Requirements You are not armored or fatigued.
You execute a maneuver that defies possibility. If the triggering effect was an enemy's attack hitting you, the enemy rerolls the attack roll and uses the lower result. If the triggering effect was you failing a saving throw, you reroll the saving throw and use the higher result.
Traits
Anything that doesn't list another rarity trait (uncommon, rare, or unique) automatically has the common trait. This rarity indicates that an ability, item, or spell is available to all players who meet the prerequisites for it. A creature of this rarity is generally known and can be summoned with the appropriate summon spell.
FortuneA fortune effect beneficially alters how you roll your dice. You can never have more than one fortune effect alter a single roll. If multiple fortune effects would apply, you have to pick which to use. If a fortune effect and a misfortune effect would apply to the same roll, the two cancel each other out, and you roll normally.
MonkAbilities with this trait are from the monk class. A weapon with this trait is primarily used by monks.