Mewtwo is being chased by Dunc, a Pokémon Hunter. Unable to trust humans, Mewtwo flees into the wilderness while Dunc tricks Virgil, the Unova League champion and a Pokémon Rescue Team operator, into helping him locate the legendary Pokémon.

Source: ANN

Note: This special aired during the TV airing of the Decolora Adventure arc.

AniDB | ANN | MAL | TVDB

Sequel: Gekijouban Pocket Monsters: Best Wishes! - Shinsoku no Genosect: Mewtwo Kakusei