Instant, W (1)
Rare
Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
You can't lose the game this turn and your opponents can't win the game this turn. Until end of turn, damage that would reduce your life total to less than 1 reduces it to 1 instead.
Illus. Mark Zug

9/25/2006: The last sentence applies only if your life total is being reduced by damage. Other effects or costs (such as "lose 1 life" or "pay 1 life") can reduce your life total below 1 as normal.
9/25/2006: If an effect asks you to pay life, you can't pay more life than you have.
9/25/2006: If your life total goes below 1, being dealt damage will not increase it back up to 1.
9/25/2006: If your life total goes below 1 or you get a tenth poison counter, you will lose the game when this effect wears off.
9/25/2006: The last sentence is not a prevention effect, but it does stop unpreventable damage from reducing your life total below 1.
9/25/2006: The last sentence doesn't change how much damage is dealt; it just changes how much life that damage makes you lose. An effect such as Spirit Link will see the full amount of damage being dealt.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern