Black Shell

Black Shells are shells of unknown origin that appear in Mario Kart Arcade GP, Mario Kart Arcade GP 2, and Mario Kart Arcade GP DX. Its effects are similar to that of a Winged Spiny Shell, though unlike a Winged Spiny Shell, it can only be fired straight and has a higher appearance rate. They explode upon impact of a wall, obstacle, or other racer, sending those caught in the blast soaring for a second. They can also be used as a triple if unlocked.

Other forms of media
One of the artworks from Super Mario Land depicts the Bombshell Koopa with a black shell. In the game, the shell detonates within a few secconds after the hero stomps on the Koopa. Some evidently high-ranking members of the Koopa Troop, such as the Fire Bros. from Super Mario Bros. 3, Black Ninjakoopa, and Lakithunder, are shown to wear non-exploding Black Shells. Additionally, in The Super Mario Bros. Super Show! Koopa Troopas, Lakitus, and Hammer Bros. were portrayed as wearing, as the episode "Mario and Joliet" showed, fire-proof Black Shells.

Trivia

 * The Black Pac-Bomb in Pac-Man World Rally is similar to the Black Shell. This is the same with the Green Shell, Red Shell, and Blue Shell, which are all similar to their respective Pac-Bomb companions.