Hiya! We made a viability rankings! A few users from the OM room and I that is!
S Rank:
Glalie-Mega [Genesect, Lucario, Linoone, Dragonite]
Keldeo [Mega Blastoise, Primal Kyogre, Masquerain]
Landorus-Therian [Talonflame, Kecleon, Mega Salamence]
Pinsir-Mega [Linoone, Genesect, Rayquaza]
A Rank:
A+ Rank:
Altaria-Mega [Genesect, Lucario, Linoone, Chatot, Flygon, Dragonite, Carracosta]
Lopunny-Mega [Pikachu, Lucario, Linoone]
Metagross-Mega[Genesect, Jirachi, Scizor]
Terrakion [Mega Heracross, Mega Lucario, Malamar, Trapinch]
Thundurus [Greninja, Kecleon, Lanturn]
A Rank:
Azelf [Kecleon, Greninja]
Chansey [Sableye, Sableye-Mega, Mew, Furfrou]
Heatran [Flygon, Latias, Latios, Primal Groudon]
Latios [Swoobat, Clefable]
Slowbro-Mega [Swoobat, Masquerain]
A- Rank:
Cresselia [Sableye, Sableye-Mega, Gliscor, Xatu, Sigilyph]
Manaphy [Masquerain, Quagsire]
Rhyperior [Quagsire, Solrock, Furfrou]
Tyranitar [Crawdaunt, Blaziken]
B Rank:
B+ Rank
Florges [Jellicent]
Garchomp [Pangoro, Druddigon, Dragonite, Tyranitar]
Gengar [Nidoking, Nidoqueen]
Gyarados-Mega [Carracosta, Crawdaunt]
Hippowdon [Ho-oh]
B Rank
Archeops [Salamence-Mega, Kecleon, Blaziken, Tyrantrum]
Magnezone [Latios, Latias]
Porygon-Z [Noivern, Chatot]
Suicune [Alomomola, Slowbro, Quagsire]
Sylveon [Mega Diancie]
B- Rank
Alakazam [Kecleon, Darmanitan, Swoobat]
Bisharp [Aerodactyl-Mega]
Chandelure [Nidoking, Rampardos, Groudon-Primal, Victini]
Goodra [Slowbro]
Mamoswine [Cloyster, Aurorus, Glalie-Mega]
C Rank:
Aerodactyl [Diancie-Mega, Tyrantrum]
Gothitelle [Gothitelle]
Houndoom [Ninetales]
Jolteon [Genesect, Nidoking]
Ninjask [Deoxys, Skarmory]
Scizor [Scolipede]
Togekiss [Altaria-Mega, Sylveon]
No D Rank, because you honestly won't use anything below this hehe!
Let us know if we missed / need to add somehting!