Giratina

Physiology
Giratina's Altered Forme is a giant, dragon-like Pokémon, with an appearance similar to that of a large sauropod. It has 6 legs, gold protrusions that look like external ribs, and golden horns on its head. Its neck has five red stripes and 4 black stripes. On its back, it has a black stripe pattern that extends to its legs. It has black wings with three red thorn-like appendages called Girasols (a rare type of opal) coming out of them. Giratina's Origin Forme is more serpentine (like an amphitheater) than its Altered Forme. Its wings are now shaped like tentacles with the red thorn-like appendages sticking out at the end. Its mouth is now behind the two appendages in front of its face. They open when Giratina roars or etc. The horns on its head are still the same. Giratina in Origin Forme has five rows of golden spikes protruding out of the torso and near the tail. Five gray and red stripes are partially overlapped by these spikes.

Natural abilities
Like some Pokémon, it has a signature move, called Shadow Force, which hits the opponent without fail even if the foe uses Protect or Detect beforehand. When in its Origin Forme, it retains its phenomenal amounts of HP, like any other Pokémon that is in their alternate formes, and it focuses on more offensive moves, and less on the defensive moves. It switches its Attack stats with its Defense stats in its Origin Forme, making it a great powerhouse. It is also a vastly powerful Pokémon that can use these benefits to fit the trainer's focus on attacking.

It will become Origin Forme when in the Distortion World, or when holding the Griseous Orb, which can be found in a secret part of the Distortion World that can only be entered through a portal in Turnback Cave (The portal will only open if you catch Giratina in the Distortion World) or get it before catching it.

In X and Y, the Griseous Orb is located in Terminus Cave on the same level where you battle Zygarde. The same goes for the Lustrous Orb and Adamant Orb.

Behaviour
Among the most complex Pokémon to understand, Giratina is both malevolent and dreaded in both it's nature and appearance. For all the fear it receives, Giratina can be merciful to less evil creatures. A decent example of it's merciful side, is that it will freely allow the player to enter and leave the distortion world, even in defeat and despite Team Galactic's previous meddling.

Evolution
Giratina does not evolve.

Pokemon Mythology
Giratina, along with Dialga and Palkia, was created when Arceus hatched from it's egg. Arceus tasked Giratina to create anti-matter. Giratina was known (other than mewtwo) to be one of the most aggressive pokemon. Because of this, Arceus banished Giratina to the Distortion World, where it supposedly would be trapped forever.

Trivia

 * No other Pokémon has the same type combination as Giratina.
 * Because of this, Giratina is the only dual type Pokémon that is weak to both of its types.
 * Along with Palkia and Dialga, their eyes resemble those of Arceus's.
 * Giratina has 6 neck spikes, 6 wing spikes, and 6 legs in its regular form; this is possibly referencing 666, the Devil's Number.
 * Also, in the Bible, Satan is referenced to be a serpent, and Giratina's Origine Forme is very serpentine.
 * Along with these resemblances, Giratina's species is the Renegade pokemon; this may also be referencing the fact that in the Bible, Lucifer became "renegade", separating himself from God, before the creation of the world.
 * However, none of these speculations have ever been confirmed.
 * In the anime, Giratina has the same roar as the monster Mothra, who initially starred in her own movie, before being absorbed by the Godzilla franchise.
 * Giratina is not the only monster to have a roar from the Toho Sound Library. Palkia, Zekrom, Reshiram and Kyurem also have roars used by monsters in the Godzilla franchise (part of Palkia's roar came from Skywalker Sound).
 * If one listens closely, Girantina's cry sounds like it has background music.
 * Giratina is currently the only Pokemon to fall down from the top of the screen at the start of its wild encounter (Platinum only).
 * At the start of the Distortion World battle in Platinum, the message says "The Distortion World's Giratina appeared!". This is another one-off, but this only appears once. From there on, references state "The wild Giratina".