You don't lose the game for having 0 or less life.
When you have 20 or more life, you lose the game.
Whenever you lose life, you gain 2 life for each 1 life you lost. (Damage dealt to you causes you to lose life.)
Other enchantments you control have shroud. (A permanent with shroud can't be the target of spells or abilities.)
Enchanted creatures you control have shroud.
Wither (This deals damage to creatures in the form of -1/-1 counters.)
Whenever this creature deals damage to a player, that player can't gain life for the rest of the game.
: This creature deals 1 damage to any target."
