Giant Red Shell
From the Super Mario Wiki
Giant Red Shells are items found in some Mario games. In Super Mario Bros. 3, the red-shelled Big Koopa Troopas wear these giant shells; Mario or Luigi can jump on these oversized Koopas, making them retreat in their shell. As with other turtle shells, they can also be picked up and kicked. They return in New Super Mario Bros. U and New Super Luigi U, where they serve the same purpose.
Giant Red Shells make a return in the Mario Strikers series as an item, along with their smaller counterparts. Working similarly to their smaller counterparts from the Mario Kart series, they can be collected and fired. The item homes into opposing team members, squishing and stunning them for a short while. After hitting its target, it randomly bounces around the stage until it wears out.