It is not possible to truly escape a black hole after crossing the event horizon, but it is possible, with the aid of teleportation, to survive one. This chance encounter in distant space did strange things to a Cosmog's body, implanting in it a tiny fragment of a black hole which grows with said Cosmog until it threatens to engulf everything around it. When this happens, the Cosmog will use its psychic powers in its entirety to rearrange the heavier elements that fused within the black hole into a shield or cocoon; by evolving into Cosmoem, it can protect the outside world from harm.

Cosmoem is an immobile pokemon, and its extreme mass and density make it impossible for any but the strongest fighting types to move it, but its beautiful, shining shell has enthralled many an onlooker; records from ancient times speak of a king who built a shrine around one, worshiping it (not without cause) as an emissary from the heavens. The location of that shrine, however, has been lost to history; many speculate that it was consumed in its entirety, together with the Cosmoem, by the black hole within it.

Yet although the specific type of encounter required makes it unlikely that most Cosmog ever evolve, and while Cosmoem arrive at their "cocoons" in a very different way than Pupitar or bug pokemon, they, too, continue to grow within. For lack of anything else to do, Cosmoem spend their time deep in thought, honing the psychic powers which allowed them to build their eight-pronged, golden frame. Perhaps, like Nebby, that ancient Cosmoem at last learned to the control the power of black holes and manipulated its extreme mass into a mobile and powerful form – and the shrine, with no god left within, was simply abandoned or repurposed.