>Deoxys's forms are game-specific in Generation III, but can be changed at will in later generations by inspecting the meteorites in
Veilstone City in Sinnoh.
Route 3 in Kanto.
Nacrene Museum in Unova.
and Ambrette Town's Fossil Lab in Kalos.
>In Platinum, the appliances are located in Rotom's Room in Galactic Eterna Building via the use of the Secret Key.
In HeartGold and SoulSilver, the appliances are located in Rotom's Room in Silph Co. which can be accessed when entering the broken elevator with Rotom as the walking Pokémon.
In Black, White, Black 2, and White 2, they can be found in the basement of Shopping Mall Nine.
In Pokémon X and Y, the appliances are found on the second floor of the Pokémon Lab in Lumiose City. Using these locations, Rotom can also change back to normal form.
>The Origin Forme is known as Giratina's natural form, which it appears in its home of the Distortion World. If it travels to the Pokémon world, it assumes its Altered Forme. Both forms appear in Pokémon Platinum, where Giratina is captured in the Distortion World in its more offense-oriented Origin Forme and will revert to the defensive Altered Forme outside of this area unless it holds the Griseous Orb.
In Pokémon Platinum it can be obtained at the Distortion World. In Pokémon Heart Gold and Soul Silver it can be found at Sinjoh Ruins holded by a Giratina. In Pokémon Black and White it can be obtained at Marvelous Birdge given by the Shadow Triad.
In Pokémon Black 2 and White 2 in can be found at Dragonspiral Tower 4F. In Pokémon X and Y it can be found at Terminus Cave at Zygarde's chamber (1F).
>Like Giratina and Deoxys's transformations are activated by an external source, Shaymin's is activated by contact with a Gracidea, whose bouquets look almost like a sleeping Shaymin. Upon changing forms, Shaymin also changes its cry.
A Shaymin in its Sky Forme will revert to its Land Forme if frozen or during night.
The Gracidea can be received in Pokémon Platinum during the player's first or subsequent trips to Floaroma Town. In Pokémon HeartGold and SoulSilver, the Gracidea is obtained at the Goldenrod City flower shop. In Pokémon Black and White, if a fateful encounter Shaymin is shown to a woman in Lacunosa Town's Pokémon Center. In Pokémon Black 2 and White 2, the Gracidea is obtained from a woman in Striaton City's Pokémon Center. In Pokémon X and Y, Gracideas are featured in one of the paintings on display at the Lumiose Museum. A female NPC located at the Snowbelle City Pokémon Center will share one of her Gracideas with the player if she is shown a Shaymin.
>Keldeo has a new form in Pokémon Black and White 2, the Resolute Form; its original form is called the Ordinary Form. Keldeo changes forms in an event in the Pledge Grove. To remain in its Resolute Form, it must have Secret Sword as one of its moves. To revert back to its Ordinary Form, Secret Sword must be forgotten.
In Gen V, if the player brings an event Keldeo with Cobalion, Terrakion, and Virizion in their party to Moor of Icirrus, they will teach it Secret Sword.
In Gen VI, if the player brings Keldeo and Meloetta to a move tutor that located in a house behind the Pokémon Center in Snowbelle City, just left of the Abomasnow, the Ace Trainer on the first floor will teach Secret Sword to Keldeo or Relic Song to Meloetta.
>If Meloetta uses the move Relic Song in battle, it changes between its Aria and Pirouette Formes, changing its typing between Normal/Psychic and Normal/Fighting, respectively. Meloetta reverts to Aria Forme when it is no longer in battle.
In Gen V, if the player brings an event Meloetta to Café Sonata in Castelia City, a musician will teach it Relic Song.
In Gen VI, if the player brings Meloetta and Keldeo to a move tutor that located in a house behind the Pokémon Center in Snowbelle City, just left of the Abomasnow, the Ace Trainer on the first floor will teach Secret Sword to Keldeo or Relic Song to Meloetta.
>The Forces of Nature—Tornadus, Thundurus, and Landorus—have alternate forms known as their Therian Formes, which are obtainable in the Pokémon Dream Radar and transferable to Pokémon Black and White 2. Their original forms are known as their Incarnate Formes. If the Therian Formes are captured through the Pokémon Dream Radar and changed to their Incarnate Formes using the Reveal Glass.
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Hope this helps!