Dummied Out: The beta version of the game (which had the working title Super Mario Kart R) had an art style more akin to Super Mario RPG, still had the Feather item from the first game, and one of the racers was a Magikoopa (presumably intended to be Kamek). In the release version, the art style changed to that of Super Mario 64, DK replaced Magikoopa and the feather was considered a Game Breaker.
Urban Legend of Zelda: It was a fairly common belief that the Green Thwomp in Bowser's Castle was a secret racer.
