Thassa's Emissary is a uncommon Enchantment Creature — Crab card from Theros (THS), collector number 68. Current market price: $0.25 (foil $0.62), TCGplayer market prices via Scryfall.
Bestow {5}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached.) Whenever this creature or enchanted creature deals combat damage to a player, draw a card. Enchanted creature gets +3/+3.