Shaymin is a mythical Pokémon that has two forms: Land Forme and Sky Forme.
* Land Forme Shaymin: This is the standard form you'll encounter.
* Sky Forme Shaymin: This form is only obtainable through specific events or trading from other games.
To get Sky Forme Shaymin in Diamond, you'd need to:
1. Obtain an event code: These codes were distributed at special events in the past.
2. Redeem the code: You would need to use the code to unlock Sky Forme Shaymin in your game. This is no longer possible as the events have ended.
However, you can trade with players who have Sky Forme Shaymin in other games, like Pokémon Brilliant Diamond or Pokémon Shining Pearl. This is the most common way to get Sky Forme Shaymin today.