Kayla's Music Box is a rare Legendary Artifact card from The Brothers' War Commander (BRC), collector number 15. Current market price: $0.23, TCGplayer market prices via Scryfall.
{W}, {T}: Look at the top card of your library, then exile it face down. (You may look at it any time.) {T}: Until end of turn, you may play cards you own exiled with Kayla's Music Box.