You don't have to play Super Mario Maker as Mario, you know.
Hidden inside Mario Maker are dozens and dozens of costumes that you can wear, all of which transform you into different Nintendo characters, as you can see in this level created by Wii U owner Jirard. Just about every franchise is represented here, ranging from favourites like Isabelle from Animal Crossing, to stranger inclusions like the Wii Fit Balance Board. While the costumes are mostly cosmetic, if you press "up" on the D-Pad, a special animation will play. Beating a level with special characters also lets you hear costume-specific fanfare, which is a nice touch.
There are two ways of unlocking costumes. You can play through the 100 Mario Challenge, and the game grants you a single random costume upon completion. Or, you can purchase an Amiibo you'd like to see within the game, and unlock it immediately that way. Every Amiibo is supported, save for Mii Fighters. Note that costumes can only be viewed in original Super Mario Bros. style levels!
So. Got any favourites? I'm in love with all the strange costumes, like the spring board one. Oh, Nintendo. You're so quirky.