Key to the City is a rare Artifact card from Kaladesh Promos (PKLD), collector number 220s. Current market price: — (foil $3.23), TCGplayer market prices via Scryfall.
{T}, Discard a card: Up to one target creature can't be blocked this turn. Whenever this artifact becomes untapped, you may pay {2}. If you do, draw a card.