Moonsilver Key is a uncommon Artifact card from Innistrad: Double Feature (DBL), collector number 255. Current market price: $5.16 (foil $41.92), TCGplayer market prices via Scryfall.
{1}, {T}, Sacrifice this artifact: Search your library for an artifact card with a mana ability or a basic land card, reveal it, put it into your hand, then shuffle.