Pokemon: Pikachu no Fushigi na Fushigi na Daibouken
English name: Pokémon: Pikachu's Big Mysterious Adventure
Genres: Adventure, Comedy, Fantasy
Type: Special, Episodes: 1
Aired: Aug 1, 2010
Studio: OLM
Source: Unknown
Rating: PG - Children
Synopsis:
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)