For the first time ever in a non-arcade Mario Kart game, there is a character in the roster who is not part of the franchise: Link from the The Legend of Zelda series, and Villager and Isabelle from Animal Crossing as downloadable DLC.
If you wait long enough hearing the Main Menu music, it will begin to play the Super Mario Kart (1992) Main Menu music as well but in a more jazzy style.
This is the first Mario Kart game that has headlights.
New Super Mario Bros. U: The Mecha Cheep appears in this game and there is a glider based on a Waddlewing.
New Super Mario Bros. Wii: One of the planes in Sunshine Airport has a logo for Propeller Toad Transport with an insignia of a Propeller Mushroom.