The Custap Berry activates when the Pokemon uses a move if the Pokemon began the turn with 25% health or less. On that turn, this Pokemon will move before other Pokemon using moves of the same priority. Higher priority moves will still always go before lower priority moves, regardless of Custap Berry. Using Pursuit against a Pokemon that is switching out does not activate Custap Berry.
Provides a one-time 80 power Ghost attack when a Pokemon holding this item uses Natural Gift.-Source