Become Revenant

When you lose the game due to an effect whose
source an opponent controls, chose a player other
than that opponent. You re-enter the game as the chosen player's teammate. Subsequently when
that opponent loses the game your team wins the
game. (When you become a players teammate they
choose any number of cards in their hand, on top of
their library, or on the battlefield under their control.
Those cards become your hand, library, and
permanents, respectively.)