Cosmog is a small Pokémon with a gaseous body similar to a nebula. The gases that make up its body range in color from violet to light blue. The very center of its body is black both in from and back. The black space on the front contains its face, which consists of beady yellow eyes, circular blue cheeks, and a small mouth. The space on the back has only a single blue dot. There is a golden half-circlet on both the top and bottom half of its body, which divides it exactly in half. Two wispy extensions containing starry specks serve as its arms. Its gaseous body makes it very light as it ties with Gastly, Haunter, Flabébé, and Kartana as the lightest Pokémon.
Its body is frail and easily blown away. However, Cosmog is carefree and doesn't seem to mind. It collects dust from the atmosphere, which allows it grow slowly. 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. In ages past, it was known as the “child of the stars”. 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. This Pokémon can be created by Solgaleo and Lunala.