Gix, Yawgmoth Praetor is a mythic Legendary Creature — Phyrexian Praetor card from The Brothers' War (BRO), collector number 326. Current market price: $4.38 (foil $10.60), TCGplayer market prices via Scryfall.
Whenever a creature deals combat damage to one of your opponents, its controller may pay 1 life. If they do, they draw a card. {4}{B}{B}{B}, Discard X cards: Exile the top X cards of target opponent's library. You may play lands and cast spells from among cards exiled this way without paying their mana costs.