The ability holder prevents any attack that has high priority if that move targets the ability holder. This includes moves like Quick Attack and moves boosted by the abilities Prankster, Gale Wings or Triage. PP is still consumed though. When this occurs, the text "[Pokémon] cannot use [Move]!" is displayed.
Moves that target all Pokémon (excluding Perish Song, Flower Shield and Rototiller) or all foes cannot be blocked by this ability. This ability also has no effect on an ally's priority moves. Status Z-moves with priority will have their Z-Power still activate. Mold Breaker, Teravolt, and Turboblaze ignore this ability.