The Spiny Shell's reign for Most Deadly Shell may have some competition with the Gold Shell. But before its Mario Kart debut, it served as a collectible item in Super Mario Galaxy and Coin producer in New Super Mario Bros. 2. In Mario Kart Arcade GP DX, this luxurious and highly dangerous Koopa shell locks onto players and rocks them with a deadly explosion. Because of the Gold Shell's impact on enemies, it's more of a rarer Item.