As you explore Alola in Pokémon Ultra Sun and Pokémon Ultra Moon, you’ll meet Pokémon new to the region that didn’t appear in Pokémon Sun and Pokémon Moon. You’ll see some familiar faces, too, including Mewtwo and other iconic Legendary Pokémon. Over 400 Pokémon appear in the Pokémon Ultra Sun and Pokemon Ultra Moon. There are Pokémon that have adapted to the Alola region’s unique environment and become regional variants, which look different from the same species in other regions. They’ll be returning from their appearance in Pokémon Sun and Pokémon Moon. Pokémon Ultra Sun and Ultra Moon are set to arrive on November 17 for the Nintendo 3DS family of systems.
Source: @Pokemon