I feel like Mest was correctly added to this battle. Isn't he, after all, a really forgettable character? The battles have all ended, so the heat of the situation disappeared, and that's when he makes a move. That's the kind of character he is to me. For all we know, he might have messed with everyone's memories.
Although I still think my development, with some random citizen rescuing Jellal without being aware of the threat he is, would have been better.