Vivien's Arkbow is a rare Legendary Artifact card from War of the Spark Promos (PWAR), collector number 181s. Current market price: — (foil $1.24), TCGplayer market prices via Scryfall.
{X}, {T}, Discard a card: Look at the top X cards of your library. You may put a creature card with mana value X or less from among them onto the battlefield. Put the rest on the bottom of your library in a random order.