Bug with the Follow The Leader OTOM - You're allowed to use megas without mega evolving (and without their stone) as long as it isn't the leader. This includes banned megas, like Mega Mewtwo-Y, Mega Rayquay, and PDon.
Replay: http://replay.pokemonshowdown.com/followtheleader-409445392
Replay: http://replay.pokemonshowdown.com/followtheleader-409445392