The Shell Cup is a cup that appears in the Mario Kart Series. first appearing in Mario Kart DS and returning in later games. This cup would contain tracks from previous Mario Kart games. It's symbol would be the Green Shell and have tracks from the Mushroom Cup or Flower Cup. It is always the first cup of the four Retro Cups.
The Shell Cup would be the third cup for the Star Open tournament series in Mario Tennis Open. It would be the counterpart for Banana Cup. It would have a Red Shell instead of the Green Shell for this game and the Red Shell would be located on the top of a tower that looks like a feature from Bowser's Castle. It could only be unlocked after beating the Ice Flower Cup. Players would play on the Bowser's Castle court and for completing it, the player will unlock the Star Cup, the final cup of the Star Open.