The Sellsword

You lose the game if your teammate loses.
When a source an opponent controls causes you
to lose life, turn The Sellsword face up, and your
opponents bid life. The player that caused you to
lose life begins the bidding with a bid of 0. Each
opponent in turn order may then top the
previous bid made. If the high bid stands, the
bidding ends and the high bidder pays life equal
to the bid, then becomes your teammate.
He'll fight for anyone.....for a price