Shells is a large Mobian Maryland blue crab with green claws and a navy blue color.

Shells is a brooding crab who exudes an intimidating aura, one that initially frightens Sonic and Tails. He is monosyllabic and says very little in general. He is also much heavier than he appears, heavy enough to smash a hole in Eggman's base. Despite his intimidating demeanour, Shells is a good person at heart, if a little blunt. Shells seems to be very fond of food, especially clam chowder.