Castle of Illusion is a side-scrolling platformer in which the player takes control of Mickey Mouse as he goes inside the Castle of Illusion in order to rescue Minnie Mouse from an evil witch named Mizrabel, who wants to steal Minnie's youth. Upon meeting and conversing with the castle's true owner and king, Mickey is told that in order to defeat Mizrabel he must find the Seven Gems of the Rainbow. Majority of the seven gems are kept within various illusion-filled worlds (known in the game as levels), and are being guarded by Mizrabel's henchmen – which are known as the Masters of Illusion. Alongside the Masters of Illusion are bizarre creatures - such as enchanted mushrooms, toy soldiers, ball-juggling unicycle-riding clowns, and armored knights that Mickey must face. After thanking the castellan and hurrying into the castle hallway, Mickey begins to search through five doors that each lead to a different level. The levels are The Enchanted Forest, Toyland, The Storm, Dessert Factory, The Library, and finally, The Castle.