Ultra Instinct

When you cast this spell as an Action, your target gains incredible reflexes as their entire body begins reacting on pure instinct. Time almost seems to pass slower for them as their mind opens up to every sensory input. They gain an extra Reaction each round. As a Reaction, the target of Ultra Instinct may choose an Attack Roll made targeting them or a Saving Throw they failed and re-roll the result. They can choose to do this after the result is revealed. They must use the new roll. If a roll is affected by Advantage or Disadvantage this re-roll is done after both rolls are initially done and only allows for a single re-roll. In addition their critical range increases by 1 as they find gaps in an opponent's defenses easier. (I.E.: If you would naturally score a critical hit on a 20 you instead score a critical hit on a 19-20)