Jimmy is a Guitarist and a Pokémon Trainer. He is known as the Wandering Guitarist but people also call him Jimmy the Pikachu Trainer. He travels around searching for strong Pikachu's to battle him. He can clearly be identified by the make-up he wears that makes him look like a Pikachu as well as the loud noise from his guitar.
He heard about
Ash Ketchum having a strong Pikachu and
Jimmy was searching for him when he encountered Team Rocket. He overheard
Meowth talking about a strong Pikachu. After searching for awhile, he found
Pikachu and wanted to battle but
Ash Ketchum had caught a cold so
Serena pretended to be
Ash Ketchum and battled him until Team Rocket showed up and tried to get both Pikachu's.
Ash Ketchum came out of the tent to see what was going on and realized what Team Rocket was up to. After fending off Team Rocket,
Jimmy realized that
Serena had tricked him but was impressed with her abilities as a trainer.
Ash Ketchum and
Jimmy decided to battle against each other for real this time but it wasn't shown in the episode as they stopped to eat before the battle took place.