In the *Pokémon Mystery Dungeon* games, you don't actually transform into a Pokémon. You are a human who has been magically transformed into a Pokémon, and you must explore the dungeons and solve mysteries to discover why this happened and how to return to your human form.
The process of becoming a Pokémon in the game is usually explained through an introductory story. The player character is usually chosen by a Pokémon to join their team and embark on their adventures.
Could you clarify what you'd like to know about the transformation process or any other aspect of *Pokémon Mystery Dungeon*? I'm happy to help!