Phyrexian Unlife is a rare Enchantment card from Secret Lair Drop (SLD), collector number 1213. Current market price: — (foil $11.07), TCGplayer market prices via Scryfall.
You don't lose the game for having 0 or less life. As long as you have 0 or less life, all damage is dealt to you as though its source had infect. (Damage is dealt to you in the form of poison counters.)