Demonlord Belzenlok is a mythic Legendary Creature — Elder Demon card from Secret Lair Drop (SLD), collector number 159. Current market price: $1.58 (foil $1.82), TCGplayer market prices via Scryfall.
Flying, trample When Demonlord Belzenlok enters, exile cards from the top of your library until you exile a nonland card, then put that card into your hand. If the card's mana value is 4 or greater, repeat this process. Demonlord Belzenlok deals 1 damage to you for each card put into your hand this way.