The Storm Blot is based on an early concept of what would happen if Oswald sided with the Shadow Blot. He was supposed to be the main antagonist for the Epic Mickey video game until he was sent to the Wasteland.
In a surprising move in on itself, Oswald himself has a dark counterpart from an earlier version of the adventure who actually supports the Blot in trying to destroy Mickey. This evil Oswald ended up merging with the Shadow Blot to become a hybrid mixture of the two villains known as the Storm Blot. It gained more power by capturing both known and unknown characters in order to obtain the hearts needed to escape the Wasteland, but the evil Oswald was eventually destroyed by Mickey. Now the real Oswald, the Jerk with a Heart of Gold that we all know and love, is making sure his evil predecessor doesn't escape from the Ink and Paint Bottle on Mickeyjunk Mountain.