From the Super Mario Wiki
The Black Circuit is a kart that appears in the Mario Kart series. It was originally a color scheme for the Circuit Special in Mario Kart 8 and Mario Kart 8 Deluxe; however, in Mario Kart Tour, it appears as a separate vehicle and is classified as a tour-exclusive High-End kart. Like with the Circuit Special, slipstreaming lasts longer and yields more points when using this kart. The Black Circuit could be unlocked during the Tokyo Tour, where it was part of a Tour Gift for Gold Pass members after getting 310 Grand Stars. Also like the original Circuit Special, the emblem is located on the hood and it uses the Slick tires from Mario Kart 8 and Mario Kart 8 Deluxe.
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