The Black Knight

When the only other players are The King, their
teammates and your teammates, reveal The Black
Knight and you all win the game. When there is
no King, you lose the game if The Black Knight
is face down.
If you would lose the game at any other time,
instead turn The Black Knight face up, remove
all commander damage and poison counters from
you, and your life total becomes 10.
If The Black Knight is face up, there is no King,
and you have no opponents, you win the game.