Shell Cup

The Shell Cup is a representation of four cups introduced in Mario Kart DS, each of which is taken from the previous Mario Kart games. Shell Cup's symbol is a Green Shell and it features tracks from previous Mushroom Cups and Flower Cups. The tracks are usually quick and simple with little hazards. It is the first of the four Retro Cups. The cup's length and difficulty is on par with the Mushroom Cup.

Mario Tennis Open
The Shell Cup also appears in Mario Tennis Open as the third cup in the Star Open tournament series. However, the shell is a Red Shell instead of the usual Green Shell. The design for the cup is a Red Shell on top of a tower that resembles a feature from Bowser's Castle. The court that players participate in this cup is Bowser's Castle.

Trivia

 * Like the Banana and Leaf Cups, every version of the Shell Cup has had a course from Mario Kart 64.
 * Both Mario Kart 7 and Mario Kart 8's Shell Cups contain one track each from Mario Kart 64, Mario Kart: Super Circuit, Mario Kart DS and Mario Kart Wii.
 * Mario Kart DS and Mario Kart 7 each had a Shell Cup that has been consisted entirely of Mushroom Cup courses, as opposed to Mario Kart Wii and Mario Kart 8 having two Mushroom Cup courses and two Flower Cup courses each. Also, the Shell Cups in Mario Kart Wii and Mario Kart 8 have the same amount of Mushroom and Flower Cup courses as the Banana Cups from Mario Kart DS and Mario Kart 7.
 * Mario Kart Wii and Mario Kart 8's Shell Cups start with the second track of the Mushroom Cup (Peach Beach and Moo Moo Meadows).
 * Mario Kart Wii's Shell Cup is the only cup that doesn't have a course from Mario Kart: Super Circuit.
 * Mario Kart 7's Shell Cup is the only Retro cup that doesn't have a Mario course.