New Super Mario Bros. Wii
During the development of "New Super Mario Bros. Wii", the developers at Nintendo decided between four characters to be playable in the game: Princess Peach, Toad, Wario and Waluigi (all suggestions made by fans). Two Toads (yellow and blue) were eventually included as playable characters in "New Super Mario Bros. Wii" due to their physical similarity to Mario and Luigi.