Cassidy's Drowzee is a Psychic-type Pokémon briefy owned by Cassidy.
In OI005: Pikachu Re-Volts, Butch and Cassidy used Drowzee to brainwash Pokémon into turning against their Trainers and obeying Butch and Cassidy. Ash's Pikachu was one of the Pokémon affected. Butch and Cassidy revealed that they stole Drowzee from their fake breeding center. Following their arrest, it is not confirmed if Drowzee was returned to its official Trainer. In the end, Misty's Togepi uses metronome and the tower explodes.