Pokemon 4Ever: Celebi - Voice of the Forest (2001)

Ash and his are transported 40 years into the past, where they meet a Pokémon Trainer named Sam and his sister Diana. They must protect the Pokemon Celebi from the evil Marauder and find a way to save the forest from extinction. This movie emphasizes the bond between humans and Pokémon: Has a Pokemon Trainer, you must watch it!