I didn't lose at all.
Lumio the Fire fang Mightyena was able to KO most of his pokemon in between one to four hits (he was like level 79 or something), then when mega metagross came out and fainted Lumio, Lulu, the level 80 perfect-IV EV-trained Altairia, dropped mega metagross' hp to about half before he crit her D:
Then Japas the Masquerain killed it with a Bug Buzz. It wasn't even a critical hit, just a Bug Buzz, and he was only level 78.
The first thing I said when I beat him was "WELL. That was definitely harder than Diantha." because she was the easiest champion I've ever faced.