Erebos's Emissary is a uncommon Enchantment Creature — Snake card from Theros (THS), collector number 86. Current market price: $0.15 (foil $0.36), TCGplayer market prices via Scryfall.
Bestow {5}{B} (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.) Discard a creature card: This creature gets +2/+2 until end of turn. If this permanent is an Aura, enchanted creature gets +2/+2 until end of turn instead. Enchanted creature gets +3/+3.