The next Rating Battle season has officially begun in Pokémon Sun and Moon, promising tons of opportunities to battle with other Trainers. In this Rating Battle season’s Special format, nearly every Pokémon from every region is permitted, except for Mythical Pokémon, some Legendary Pokémon, and Ash-Greninja. You’ll battle in Single Battles, and all Pokémon will be set to Lv. 50 for the duration of the battle.
The big twist for this format is the limit on which items your Pokémon can hold—only Z-Crystals will be permitted! This format is sure to be fast-paced and exciting for everyone. See the Special format’s regulations for details. The Rating Battle seasons are a great way to practice for upcoming Pokémon Championship Series events, as well as to have fun battling in other formats.
Source: Pokémon Global Link