Key to the Side-Door is a uncommon Artifact card from The Hobbit (HOB), collector number 175. Current market price: $0.27 (foil $0.28), TCGplayer market prices via Scryfall.
{2}, {T}: Target creature can't be blocked this turn. {1}, {T}, Discard a legendary card with the same name as a legendary permanent you control: Draw two cards.