Skeleton Key is a uncommon Artifact — Equipment card from Shadows over Innistrad (SOI), collector number 263. Current market price: $0.27 (foil $1.68), TCGplayer market prices via Scryfall.
Equipped creature has skulk. (It can't be blocked by creatures with greater power.) Whenever equipped creature deals combat damage to a player, you may draw a card. If you do, discard a card. Equip {2}