I haven't tested it yet as I still need to level my Bergmite, but I'll be using Baton Pass Vaporeon (with Acid Armor and Aqua Ring), Amnesia Mega Venusaur (with Leech Seed, Giga Drain, and Sludge Bomb), Rain-Rest Goodra, Dragon Dance Tyranitar, Delphox to hit Steel types like Ferrothorn, Aegislash, and Scizor, and Avalugg to cover physically offensive Dragon types like Mega Salamence and Garchomp.
I'm expecting Garchomp, Mega Salamence, Mega Gengar, Mega Lucario, Ferrothorn, Mega Charizard (either one), (Mega) Scizor, Aegislash, and Tyranitar to all be popular in this competition.