Pokemon Season 5 - Episode 241 – Hocus Pokémon

A Pokémon magician named Lily attempts to create a magic spell, but as well as needing Pikachu, is missing one ingredient; a tear from an Aipom. Team Rocket steal Lily's spell book and try to get Aipom to shed a tear without force. After beating Team Rocket, however, the spell fails and Ash is turned into a Pikachu.