Arena | Magic: The Gathering
Formats Arena is Legal in
Official Oracle Text for Arena
Official Rulings for Arena
10/4/2004 : In multiplayer games, you can choose a different opposing player each time it the ability is activated.
10/4/2004 : Either or both creatures can be tapped prior to using the ability and it still works.
9/25/2006 : If either target is illegal at the time the ability resolves (whether because it has left the battlefield, because it has gained Shroud or Protection, or for any other reason), the ability taps the remaining target, but no damage is dealt. If both targets are illegal, the ability is countered.