Shadow Slice is a common Sorcery card from Gatecrash (GTC), collector number 77. Current market price: $0.04 (foil $0.34), TCGplayer market prices via Scryfall.
Target opponent loses 3 life. Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)