Avacyn, Fateful Savior

Indestructible, Vigilance
When Avacyn, Fateful Savior enters the
battlefield, if you have 15 or more life, sacrifice it.
Fateful Hour — As long as you have 5 or less life,
you can't loose the game and your opponent
can't win the game. Creatures you control have
vigilance and first strike.