These new forms are likely only to work while in Platinum.
Originally Posted by You-Know-Where
The game will feature Giratina as its mascot and introduce its Origin Forme, as seen in Giratina to Sora no Hanataba: Shaymin. Its initial form is referred to as its Another Forme. The new storyline will involve a disturbance atop Mt. Coronet, as a portal to the "Ruined World" is opened and Sinnoh's climate becomes colder. The trainers have been given new outfits to suit the colder climate.
The legendary Pokémon Shaymin, which will be distributed as part of admitance to the film Giratina to Sora no Hanataba: Shaymin, will also have an alternate form in Platinum, known as its "Sky Forme", a dual Grass and Flying-type Pokémon. When traded from Diamond or Pearl to Platinum, Shaymin will transform from its regular Land Forme into its Sky Forme with the use of a new item in Platinum. It is not yet known what role Shaymin plays in the story of Platinum. When the special Regigigas that is given out with a pre-order ticket for Giratina to Sora no Hanataba: Shaymin is traded from Diamond or Pearl to Platinum, it activates an event that makes Regice, Regirock, and Registeel available in Platinum.
Silhouette images of five unknown Pokémon have been released by the official website. They are described as "mysterious Pokémon" and are either five completely new Pokémon, or new forms of old Pokémon. The items to obtain them will be given away in stores and over the WiFi connection from September 28 to November 4, 2008.
The Battle Frontier, which was first introduced in Pokémon Emerald, appears again in Platinum. The game also features brand new WiFi functions such as mini-games the player can play with people from all over the world.