The Sellsword

If your teammate wins the game or loses the
game, you also win the game or lose the game.
If you are the only player and have no teammate
you win the game.
If a source an opponent controls causes you to
lose life, you may reveal The Sellsword. If you do,
each player may bid life. You start the bidding
with a bid of 0. In turn order, each player may
top the high bid. The bidding ends if the high bid stands. The high bidder loses life equal to
the high bid and becomes your teammate.