Chromeshell Crab is a rare Creature — Crab Beast card from Commander 2011 (CMD), collector number 41. Current market price: $0.35, TCGplayer market prices via Scryfall.
Morph {4}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.) When this creature is turned face up, you may exchange control of target creature you control and target creature an opponent controls.