As first revealed by Japan's CoroCoro Magazine, Giratina has two forms. The first (Altered Forme) is the form that appeared in Pokémon Diamond and Pearl. In this form, Giratina has a large, gray, centipede-like body with six short, thick legs. Its legs have gold claws and gold bands on them. It has a tail and a thick black stripe running vertically along the front of its body. There is a series of red horizontal stripes running across the large black one. Three gold half-rings circle the back half of Giratina's neck at the same points that three of the red stripes are at on its front, resembling a ribcage. On its back are two large, black wings that are decorated with red, conical objects that also could be claws. The wings seem oddly out of place, due to the fact that Giratina seems far too heavy to fly effectively. The wings also seem to be ghostly, as they can change shape as if they were made of a liquid or gas.

Giratina's head and eyes resemble those of Dialga and Palkia, causing many to theorise that it is related to the two. This assumption is confirmed in Pokémon Platinum.

The second is a new Origin Forme which made its debut in Giratina and the Sky Warrior. It uses this form when travelling through dimensions other than ours, such as the Distortion World, its home. The form-altering is triggered by a change of gravity. This form is more serpentine than Giratina's Altered Forme. The Origin Forme of Giratina has six black, ghostly streamers on its back that each have a bright red spike at the end. Its mouth is hidden by the head plates, which swing open sideways when the mouth is opening. Giratina's legs have been reduced to spike-like protrusions. There are four more golden spikes near the edge of the tail. The three gold half-rings in this form can be used to grip objects. This version of Giratina also appears in Pokémon Platinum, and can be activated outside of the Distortion World if it is holding a Griseous Orb.