Book Of Exalted Deeds

At the beginning of your end step, if you didn't
attack this turn you may pay {p/c}. If you do,
Venture Into The Dungeon.
{1}{w}, Exile this artifact: If you've completed two
or more different dungeons, until end of turn all
damage that would cause target opponents life to
drop below 1 instead puts it at 1, and you gain
protection from everything until end of turn.
You and the target can't lose the game this turn.