Cameos
R.O.B.
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One of the unlockable characters is R.O.B., the Robotic Operating Buddy NES accessory. In the Japanese version, ROB is "Famicom Robot" and appears in his original Japanese colours.
The ROB-BLS kart is based on R.O.B.'s Stack-Up set, with trays surrounding him. The ROB-LGS kart appears to stand for "R.O.B. Legs".
Cameo Karts
Several of the karts are references to other games:
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Clown Car Copter
Bowser's Clown Car Copter is based on the Koopa Clown Car that he used in Super Mario World and Paper Mario.
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Rambi Rider
Donkey Kong's Rambi Rider car is based on Rambi, Donkey Kong's animal buddy from Donkey Kong Country.
Nintendo DS Battle Course
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One of the Battle courses takes place on a giant Nintendo DS.
Super Mario Bros. 3 Icons
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When you start the game, the icon that appears next to the 1-player mode is Mario's head from Super Mario Bros. 3. When the multiplayer game is loading, Mario and Luigi's 8-bit heads both appear, overlapping each other.
Wario Stadium
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In Wario Stadium, 8-bit sprites of a Super Mushroom and Star Man from Super Mario Bros., as well as the NES font, all appear on displays around the course.
Shroom Ridge
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On the Shroom Ridge track, the trucks feature sprites of Cheep Cheep from Super Mario Bros. 3 and Berries from Super Mario World on the side.