Gabe is correct!
Instant Special Abilities > Fight Each Other
How to Use
If two heroes (or two evil characters) are forced to fight each other, this is called a side battle. In a side battle, each player involved in the original battle controls the characters on one side of the side battle. The characters which must fight are selected by the player of the side battle ability and placed into the side battle in any order. If only one selected character was already in battle, then its current controller retains control of that character in the side battle. If both of the selected characters are being controlled by the same player in the original battle, the player of the side battle ability chooses which one he will control in the side battle. The player that controls a character controls any banding special abilities (if applicable). However, characters in a side battle cannot band to characters already in the Field of Battle. If one or more characters already in the field of battle are selected to fight in a side battle, their special abilities do not reactivate.
If the side battle ends in a mutual destruction, all cards in the side battle are discarded. If the side battle does not end in mutual destruction, the battle is resolved as follows:
• Losing characters are discarded along with any enhancements played on them.
• Characters not discarded or removed from the side battle that came from the original battle return to the original battle, including any enhancements played during the side.
• Any other characters not discarded or removed from the side battle return to their owner’s territory. The active battle then transfers back to the original battle.
