The Phantom Blot, known in Epic Mickey as the Shadow Blot, is a large anthropomorphic ball of darkness. He is a mixture of Paint and Thinner (more commonly known as ink). The Blot cannot be befriended with paint or destroyed with thinner and is the most dangerous enemy. Thinner does, however, cause the Blot to temporarily melt, as seen in Epic Mickey's intro, but can later reform into its original state.
The Phantom Blot appears in Disney Kingdoms, and is given the title "Ruler of the Shadow". The Phantom Blot is known as the first Shadow ever, and was once a Human but, due to his power, mutated into a large creature comprised of inky darkness.
The Phantom Blot first appears in Frontierland, and in the game's opening cutscene. The Blot created the portal to the Disney Kingdom, and sucked You into it. You encounter the Blot again at X Middle School, where it has taken up residence. Instead of fighting him as the boss at the school, Yzma is fought instead. The Blot appears for a third time in Sugar Rush, where it and Turbo have taken over. Like in X Middle School, the Blot abandons this world before the fight. The Phantom Blot appears for a final time in The World That Never Was, the final world. He has taken over the entire area, and covered it with his Blotling minions. Here, he is finally fought.
In battle, the Blot creates illusions of all the past bosses, although in a random order, and uses attacks that they did, but incorporates thinner into it somehow. When he attacks, he shoots thinner and paint at You. To be defeated, he must be attacked by magic after reverting back to his original form after using an illusion. After he is beaten, his face appears in a pool of his goop, and is sucked down a drain, presumably dead.