Giant Red Shell
From the Super Mario Wiki
Giant Red Shells are items found in many Mario games. In Super Mario Bros. 3, the red-shelled Gargantua Koopa Troopas wear these giant shells; Mario can simply jump on these oversized Koopas and make them hide in their shell, which he can then pick up and kick, as with normal Koopa shells. They return in New Super Mario Bros. U and New Super Luigi U, where they act the same.
In Super Mario Strikers and Mario Strikers Charged, Giant Red Shells, as well as their smaller counterparts, are items that players can use. When collected, Giant Red Shells can be shot at the opposing players. It homes into one of the opposing team members and spin over them, which squishes them, stunning them for a short while. It homes in only once, however, and after it hits its target, it spins around the stage randomly, unlike the normal Red Shells, which home into multiple players, but hit only once.