Pokémon Sun and Moon - Poor mon's OU

Smogon tiers are largely based on usage stats on Pokémon Showdown.

IIRC, OU Pokémon are those that you have a 50% chance of encountering after 20 battles (which translates to ~3.5% usage). UU Pokémon are the ones that get used less often. NU are used even more rarely.

This is the generation that UU is reduced to cinder (until the bans start kicking in, also remember that Black Kyurem was UU for all of like 2 seconds before its ban)