cosmog
Pokémon #789 in the National Pokédex, a Psychic type legendary Pokémon.
It is extremely rare, yet nearly useless in battle. Evolves into Cosmoem at level 43, and then into Solgaleo or Lunala at level 53, depending on which version it evolves in.
Lillie keeps one in her bag, which she calls Nebby (or in Japanese, ほしぐもちゃん Hoshigumo-chan).
In the Sun and Moon anime, Nebby was primarily cared for by Ash, though he shared the responsibility with the rest of his classmates. After it evolved into its final form, Ash and company discovered it was in fact the legendary Pokémon Solgaleo, and tended to refer to it by its proper name.
Japanese name: Cosmog