Pokemon: Pikachu no Fushigi na Fushigi na Daibouken
English title: Pokémon: Pikachu's Big Mysterious Adventure
Japanese title: ピカチュウのふしぎなふしぎな大冒険
Type: Special
Episodes: 1
Source: Game
Genres: Adventure, Comedy, Fantasy
Studios: OLM
Duration: 21 min
Rating: PG - Children

While being let out to play by their trainers, Pikachu and Piplup wind up separated from their Pokémon friends and wind up travelling with a Skitty into a strange dimension, unknowingly followed by Croagunk, Team Rocket's Pokémon and a Marill that's desperate to have someone hear her sing...

(Source: Bulbapedia)