Sanctioned Duel

When Sanctioned Duel enters the battlefield,
choose two players. Creatures those players
control can only attack the other player or planeswalkers the other player controls. Those
players and permanents they control other than Sanctioned Duel both have protection from each player you didn't choose. If one or both of those players loses the game, exile Sanctioned Duel.
Planeswalkers squabble, Arbiters write up terms, prizes
are wagered and worlds burn.