Ob Nixilis, Captive Kingpin is a mythic Legendary Creature — Demon card from March of the Machine: The Aftermath (MAT), collector number 91. Current market price: $22.25 (foil $28.79), TCGplayer market prices via Scryfall.
Flying, trample Whenever one or more opponents each lose exactly 1 life, put a +1/+1 counter on Ob Nixilis. Exile the top card of your library. Until your next end step, you may play that card.