The Kingslayer

When the only other players are The King , their teammates and your teammates, reveal The Kingslayer and you all win the game. When there is no King you lose the game.

If you kill The King while The Kingslayer is face up you then become The King.
If The King kills another Knight or a Citizen flip over The Kingslayer.
While The Kingslayer is face up you gain "During your combat phase creatures you control gains Vigilance, Trample, Indestructible,+1/0 , and have to attack The King if able."