The gameplay mechanics pivot on the idea of Paint, and Thinner. At the beginning of the game, Mickey picks up a magic paintbrush that can fire either Paint or Thinner in streams. Certain objects in the world are constructed from "toon," a material that can be either erased using Thinner, or filled in using paint. This forms the base for nearly every puzzle in the game. Toon is recognizable, as it will always be more colorful than the surrounding environment, and once you've recognized that something is Toon, you know you can remove it. Something that can be filled in will always leave a silhouette behind as well, so that it's easily recognizable where you can paint something in.
Some situations will call for one of the two choices, specifically, but you will often have a choice of which to use. The game's enemies can be destroyed by using Thinner or made friendly by using Paint, and many puzzles can be solved by using one or the other. The game will take a slightly different path, placing you in the role of either Hero or Scrapper, depending on whether you choose to use Paint or Thinner in the majority of situations, putting their morality system in the spotlight once again.
Beyond that mechanic, you can jump and use a spin attack to smash enemies or objects in the world, and the game plays mostly as a standard 3D platformer. There are plenty of collectible items to obtain as well, many of them optional, to give the player tasks to do in addition to advancing the main story, and all of the tasks you're given, both optional and required, are added as "quests," which can be viewed in your pause menu. This works as a great way to organize the things you have to do. The game doesn't often let you know when you're about to go past a point where you can't turn back, which can unfortunately make it easy to fail quests you had planned to come back to. The great thing about the quests, however, is that the number of optional quests provided are a great way to add challenge for those that want it. Some of them are downright punishing, whereas the main game tends to be much simpler, to remain accessible to a wider and often younger audience.
Finally, to add one last bit of variety, to travel between levels, you jump through projector screens, which each catapult you into short 2D levels where all you can do is run and jump, all done in the style of vintage Disney cartoons. (Such as Steamboat Willie, which is literally one of the projector screens you go through.) This is an excellent way to break up the gameplay with something that has a much more retro feel, both visually and in terms of the gameplay, and because they're short levels, they never feel like they're taking away from the rest of the experience.
Epic Mickey has many different gameplay elements at work, all dressed in something that is primarily a standard 3D platform adventure game. It does an excellent job of providing a lot of variety without ever being too busy, and the main elements of the 3D world, where you can always count on coming back to, are all beautifully executed.