Pokemon Fushigi no Dungeon: Magnagate to Mugendai Meikyuu
English name: Pokémon Mystery Dungeon: Gates to Infinity
Genres: Adventure, Fantasy
Type: ONA, Episodes: 2
Aired: Nov 1, 2012
Studio: OLM
Source: Game
Rating: G - All Ages
Synopsis:
A boy awakens to the sound of someone crying for help. Looking around he notices he is on a body of water. Upon looking at his hands, he realizes he has been transformed into an Oshawott. He panics, and then finds himself plummeting toward then ground. He then wakes up again to find himself in a forest, with a female Pikachu leaning over him, asking if he's okay.

(Source: Bulbapedia)