Say a Pokemon uses mirror move and the move the other Pokemon had previously used was also mirror move. Would it just say the move failed, or would it create a loop as the Pokemon continuously tried to use mirror move?
It will fail for the second Pokemon to use Mirror Move.
Mirror Move will fail if the target did not make a move selection in the round before the use of Mirror Move, switches out during the round Mirror Move is used, or if the opponent's last move used was Mirror Move.
-Bulbapedia
