Cosmoem is a Pokémon in the shape of a translucent, dark blue orb with a starscape pattern set in a solid golden shell structure, which is made up of four ellipses intersecting each other in an asterisk shape, and another intersecting the former four along the middle. At the center of the main body is a much smaller black core with a blue and a pink marking on the front and an orange semicircle on both sides, giving it the appearance of a sleeping face. The shape also looks like an eye.
Encased in its sturdy, cocoon-like shell, Cosmoem is unable to move. In Pokémon Refresh, it cannot eat. It grows as it absorbs light, and its body is warm to the touch. In ancient times, it was worshipped as the "cocoon of the stars" by the people of Alola.
With its pre-evolution weighing in at .1kg and Cosmoem at 999.9kg, the evolution from Cosmog to Cosmoem is the largest increase in weight due to evolution with an increase of 999799.99%.
Requiring 43 levels to evolve from Cosmog and just 10 more to evolve into either Solgaleo or Lunala, Cosmeom has the lowest relative second-stage evolution requirement, at around 23%.
Cosmoem has characteristics of both a stylized sun and a stylized moon, having rays and a pair of crescents, respectively. Given its description, it seems to be an embodiment of star formation in general. It may also be based on the idea of the world egg. When viewed from the front, its shape resembles an eye.