Cassidy operates as a Team Rocket agent in the Sinnoh desert during the Diamond & Pearl series episode "Sleight of Sand!". Assigned by Dr. Namba to capture a Hippowdon, she partners with Butch. Dr. Namba supplies them with a specialized Rhyhorn-shaped robotic vehicle designed for sandy terrain and equipped with a mechanical arm to seize targets. Cassidy confronts Ash, his companions, and rival agents Jessie, James, and Meowth. Her Granbull battles Jessie's Seviper and James's Carnivine. Granbull bites Seviper but is then hit by Carnivine's Bullet Seed. Carnivine dodges an attack from Butch's Shuckle, causing Shuckle's Sludge Bomb to accidentally strike Hippowdon. Enraged, Hippowdon retaliates with Double-Edge, defeating Granbull, Carnivine, and Shuckle. A subsequent Sandstorm from a Hippopotas and Hyper Beam from Hippowdon blast Cassidy and Butch away alongside Jessie, James, and Meowth. Cassidy maintains her characteristic rivalry with Jessie throughout the mission. She criticizes Jessie and James, asserting Giovanni assigned only her and Butch to Sinnoh operations, deliberately excluding the trio. This provokes Jessie and fuels their direct clash during the capture attempt. Cassidy further antagonizes Jessie by using the Rhyhorn vehicle's horn as a projectile to destroy Jessie's Slowbro-shaped mecha.