Ominous Lockbox is a rare Artifact — Clue card from Alchemy: Murders at Karlov Manor (YMKM), collector number 8.
As Ominous Lockbox enters, secretly choose a number between 1 and 20. When an opponent casts a spell with mana value equal to the chosen number, sacrifice Ominous Lockbox. If you do, copy that spell, and you may choose new targets for the copy. {2}, Sacrifice Ominous Lockbox: Draw a card.