The Ultra Beasts introduced in Pokémon Sun and Moon are the following:
Ultra Beasts are unidentified Pokemon that live in an alternate dimension.
The male generic name is Sun and the female is Moon
To start the Looker side quest in Pokémon Ultra Sun and Ultra Moon, first complete the main story and become the Champion. Afterward, visit the Aether Paradise and speak to Looker, who is located in the basement area near the entrance to the Ultra Beast research lab. He will ask for your help in investigating the Ultra Beasts, which leads to a series of encounters and challenges involving them. Be sure to check in with him regularly as you progress through the quest.
Celesteela is a Steel-Flying type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Xurkitree is an Electric type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Nihilego is a Rock-Poison type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Buzzwole is a Bug-Fighting type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Pheromosa is a Bug-Fighting type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
Guzzlord is a Dark-Dragon type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.
It is possible to get all Pokemon in Ultra Sun and Moon through methods like Wonder Trade.
It evolves from its lower forms, Cosmog and Cosmoem. It can also open portals to other dimensions; specific examples in the game allow you to travel to the dimension where Ultra Beasts live, and also to the alternate dimension of the opposite game (Moon, if you are playing Sun), to obtain Cosmog). (A different one from the one that evolved into Solgaleo.)
Kartana is a Grass-Steel type, and it was introduced in the Generation 7 games, Pokemon Sun and Pokemon Moon.