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 warp itself and those close to it, as well as 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. Cosmog can be created by Solgaleo and Lunala.
As seen in the anime, whenever Cosmog cries it emits a high-pitch scream.