Cosmog is a small Pokémon with a gaseous body similar to a nebula. It has two wisp-like extensions that serve as arms and an ellipse running down its body. Its front and back are black in color. It has yellow eyes and two blue cheeks. In behavior, Cosmog has an overly trusting nature and it immediately takes a liking to whoever shows it kindness, even when that person doesn't have the best intentions for it.
Cosmog has the ability to open Ultra Wormholes, but only when under stress. This process is very dangerous for Cosmog, and the use of its powers can leave it immobile for extended periods of time. Cosmog is theorized by the Aether Foundation to be a type of Ultra Beast, and its name was coined by one of the professors at the Foundation.[1] Cosmog can be created by Solgaleo and Lunala at the Lake of the Moone/Lake of the Sunne.
Cosmog first appeared in the Sun & Moon arc, under the ownership of Lillie. It is nicknamed Nebby. It was first seen escaping from Lillie's bag and running off to Mahalo Trail, where it was attacked by wild Spearow. When Moon stepped in to save it, Nebby broke the bridge they were standing on, causing both to fall towards the water until they were saved by Tapu Koko.