Dracolich

At the beginning of your upkeep, this enchantment deals 5 damage to any target. At the beginning of each end step, your life total becomes 5. Creatures without flying can't attack you.

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.)