Kythera, The Final Protector

If you would lose the game, you may cast Kythera, The Final Protector, without paying its mana cost. Set your life total to 15.

• As long as Kythera is on the battlefield, damage that would reduce your life total
below 1 instead reduces it to 1.
• At the beginning of your upkeep, sacrifice a legendary permanent you control. If you can’t, you lose the game.