invincibility

Cumulative upkeep—Pay 2 life. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) When this land enters, sacrifice a land. Creatures you control can't attack. Prevent all damage that would be dealt to 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.)