Pokémon Season 4 Episode 49

40 years in the past, the Legendary Celebi flees through time to escape a poacher, accidentally bringing a young boy named Sammy with it. In present times young Sammy encounters Ash and friends in the same forest. They soon discover Celebi, and when a Team Rocket agent arrives to capture Celebi, they must evade the agent and keep Celebi safe while it recovers from its last encounter.