Umbra Stalker is a rare Creature — Elemental card from Eventide (EVE), collector number 48. Current market price: $0.45 (foil $2.77), TCGplayer market prices via Scryfall.
Chroma — Umbra Stalker's power and toughness are each equal to the number of black mana symbols in the mana costs of cards in your graveyard.