Barroom Brawl

• WOTC Official Reminder Textofficial rules
  Fight — Each of those creatures deals damage equal to its power to the other.

• WWizards of the Coast2022-06-10
  Official Ruling
  Each copy of Barroom Brawl also includes the opportunity to create a copy, so as long as there are legal targets available and the copies keep successfully resolving, the brawl can continue.
• WWizards of the Coast2022-06-10
  Official Ruling
  If the opponent to your left chooses to copy Barroom Brawl but not change its targets, both targets will probably be illegal as the copy tries to resolve (at a minimum, both targets would have to survive and switch controllers in response to still be legal targets for the copy), and the player to their left will not be able to copy it.
• WWizards of the Coast2022-06-10
  Official Ruling
  If both targets are illegal as Barroom Brawl attempts to resolve, it does nothing. No copy will be created.
• WWizards of the Coast2022-06-10
  Official Ruling
  In a two-player game, the other player is the opponent to your left.
• WWizards of the Coast2022-06-10
  Official Ruling
  The opponent to your left may choose the creature they control that was part of the original fight as the first target for their copy, even if it would die after the original spell is done resolving. If it does die, however, it will be an illegal target as the copy tries to resolve.
• WWizards of the Coast2022-06-10
  Official Ruling
  If one target is legal and the other is not legal as Barroom Brawl resolves, neither creature will deal damage. However, the opponent to your left may still choose to copy Barroom Brawl.

Rulings via Scryfall