Shambleshark is a common Creature — Shark Crab card from Gatecrash (GTC), collector number 193. Current market price: $0.21 (foil $0.31), TCGplayer market prices via Scryfall.
Flash (You may cast this spell any time you could cast an instant.) Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)