I won by a glitch with a half Health Umbreon VS a Granbull and Garchomp in the battle frontier.
I was in the Sinnoh Battle frontier (Battle factory), I had an Umbreon, Leafeon, and I can't remember what else (It really doesn't matter). I was against a Tangrowth, Garchomp, and Granbull. Umbreon was put to sleep at about half health, so I switch it out. After my second Pokemon got KO'ed, I had to switch it back in, and then Leafeon got KO'ed... So it was a sleeping half health Umbreon VS a full health Garchomp and a low (about 1/4) health Granbull. It woke up the next turn and got hit by Return bringing it to 3 HP, it KOed Granbull with Payback (Highest offensive move it had) and killed Garchomp in the next... 12 turns when it refused to stop using Snadstorm. xD
Worst of all, the leftovers I had let me survive the sandstorm and recovered my health back to about half.
I still have that match saved as my battle video...