[CONJUNCTURE: Theory posts are going to be focused purely on individual theories of mine. Humor based posts will be titled "Blog #"]
Theory #1: Mickey and the Mouse
The Photo-Negative Mickey suit is the Face of this game, so it must be important to the plot. A lot of people have been saying it is a mispainted suit, but I believe that the real mispaint is Suicide Mouse; as he is not black and white, but simply much darker than the normal Mickey Mouse. (For comparison, see Unknown Cam 2, and the Mickey head in it. Also, Suicide Mouse has really dark red pants.) No, the Photo-Negative Suit was vandalized, and the vandal used the suit to spread it. What is it? Why, the brain parasite that got Treasure Island Abandoned by Disney in the first place.
It's quite simple. Steal a spare suit, spray paint it, and then walk around the park as if you were a real mascot. By the time you are captured and detained by guards, it would be too late; the suit, and subsequently everyone who touched it (Want to take a Picture?) would be infected with the eggs, released into the suit by sweat. The suit was then thrown into storage, as Disney would be A. too lazy to destroy it and/or B. get it destroyed, as knowledge of its existence would be bad publicity. Why? Because, that would mean that someone managed to sneak in, steal from the Mascots only room, and then parade around the same park in a repainted suit.
Also, brain parasites don't evolve to inhabit a place in 10-15 years. (The island opened in 1979, and closed in 1999, and the average parasite takes >5 years to develop noticeable symptoms.) It would have to had been brought there.
Theory #2: S is for Stealing
Puritysin frequently mentions in her videos (when she reviews fan theories, that is) that the SSA might have stolen something from Treasure Island. Perhaps, in their haste to leave, and possibly in an attempt to save their skin, they dismantled some of the suits. (Specifically, Donald, Daisy, and Acephalous.) Also, Donald is called "Disembodied". Might the SSA have made him that way? Say, by stealing his (and Daisy's) bodies as evidence, only to discover that once they left the island, the bodies stopped moving? Perhaps Mickey wants his friend back. Also, Puritysin confirmed that Henry met the Face in Pirate Caverns. Before Henry met the Face, it was a whole. It was not a suit either; no, it was a statue, meant to stand by the entrance and greet visitors. It's far too small for an adult human to fit inside it, after all, and Disney would not dare hire a child (legal reasons) nor tailor a suit to a midget (Again, bad publicity). It attacked Henry, who dismantled it in the scuffle, leaving it in its current state, and Henry managed to escape; but not before the Face claimed a trophy of war: Henry's eyes.