The Shadow Blot is a supporting antagonist in the Kingdom Hearts Unlimited Saga, first appearing in "The Journey" as one of several bosses fought in the last boss rush leading up to the Final Battle against the Horned King on Bald Mountain. He later returns in "Return of the Keyblade" as part of the Grand Army of Darkness led by Emperor Palpatine for the events of the Final Battle in the Keyblade Graveyard.
One of several fragments of the Great Evil that were scattered across the universe during Chernabog's fall to the depths of Bald Mountain, the fragment that would become the Shadow Blot originated as a mindless mass of gelatinous shadowy ooze, consuming anything in its path and leaving nothing but lifeless rock and figuratively heartless statues in its wake. It was sealed away in a moonbeam crystal prison by the High Council and locked deep within the lowest dungeon in Disney-Land's High Castle, intended to never be released for centuries to come. However, when the world was attacked by the Darkhearts led by the Horned King and its keyhole unlocked as per his plan to eventually ascend to godhood, his lieutenant the Phantom Blot was able to uncover the crystal prison containing the Shadow Ooze and take it with him back to the Forbidden Mountains where he would keep it as a secret weapon in his desire to follow his master into greatness. Eventually, during the Final Battle of the End of Existence, the Phantom Blot would shatter the crystal and invite the Ooze contained within it to merge with him so that the two could become one as a monstrous shadow of Lord Chernabog's might upon the worlds, with the Phantom Blot's personality in control, of course. Instead, he was consumed entirely by the Fragment's greater will and was transformed into the vessel for a new being, the Shadow Blot, who aided his original self Chernabog and the Horned King's forces in trying to do the heroes in.