The Griseous Orb is a hold item only available in Pokémon Platinum. After defeating the Elite Four and Champion, you can access the Spring Path which leads to Turnback Cave. In this particular area, the player has to navigate their way through the cave to reach Giratina's room, and enter the Distortion World from there. Eventually you will find an item: the elusive Griseous Orb.
The Griseous Orb is a multi purpose item to be held by one particular Pokémon - Giratina. It is used to increase the power of Giratina's attacks (particularly Ghost and Dragon), and to allow Giratina to change appearance freely - once equipped with the orb, Giratina transforms into its Origin Forme. When the orb is removed, Giratina reverts back to its Alternate Forme.
The Griseous Orb's primary effect still works when battling over WiFi, however its secondary effect (altering forms) does not.
The Griseous Orb can be obtained via the Sinjoh Ruins Event. If Giritina is chosen the baby Giritina will emmerge holding the Orb.
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