Voidwalk is a uncommon Sorcery card from Gatecrash (GTC), collector number 55. Current market price: $0.25 (foil $0.94), TCGplayer market prices via Scryfall.
Exile target creature. Return it to the battlefield under its owner's control at the beginning of the next end step. 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.)