Noted as both the Super Shell and the Blue Shell, this power-up appears mostly at locations that already have shells within them, so places with a lot of Koopa Troopas and the like will see them occasionally. Some Koopa Troopas even wearing them themselves. Upon getting this item, the user wears this shell, powerful enough to smash bricks and knock down enemies with a running start, bumping off walls without losing speed. The shell also helps the user in the water, making swimming feel more light weight and quick! Probably not the Blue Shell you're thinking of.