Mystery Key is a uncommon Artifact — Equipment card from Commander Legends: Battle for Baldur's Gate (CLB), collector number 85. Current market price: $0.18 (foil $0.29), TCGplayer market prices via Scryfall.
When equipped creature deals combat damage to a player, sacrifice this Equipment. If you do, draw three cards. Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)
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