Serpent of the Endless Sea is a common Creature — Serpent card from Magic 2010 (M10), collector number 70. Current market price: $0.29 (foil $1.28), TCGplayer market prices via Scryfall.
Serpent of the Endless Sea's power and toughness are each equal to the number of Islands you control. This creature can't attack unless defending player controls an Island.