- “SHOW ME WHAT YOU GOT! I WANT TO SEE WHAT YOU GOT!”
- —A Cromulon to the inhabitants of Earth[src]
Cromulons are a species of planet-sized beings shaped as giant human heads, and are native to the Signus-5 expanse. They are encountered in the episode Get Schwifty, where they are the primary antagonist.
According to Rick Sanchez, the Cromulons "feed on the talent and showmanship of less-evolved lifeforms". They do this by capturing planets with intelligent lifeforms on them, teleporting these planets to the expanse of the universe they inhabit, and run a reality television show named Planet Music, in which these planets compete to perform music which satisfies them. Planets that lose or are disqualified are disintegrated by a massive plasma ray cannon. When Rick and Morty win Planet Music, the Cromulons mention that they had run 988 consecutive seasons of the show, and that upon Earth's performance, they have decided to bring their musical reality show to its conclusion.
The Cromulons are powerful and large enough that a single Cromulon can cause drastic weather changes such as natural disasters to planets by simply getting near them. It is implied that, despite the influence that a being the size of a Cromulon would have on a planet's cycle of nature, that they are able to manually control their effects on a planet based on their level of satisfaction. They are able to seamlessly fly through space, as if they have their own field of gravity. This could explain why their presence could cause earthquakes powerful enough to cause massive sinkholes, as well as tides receding far beyond their normal shores, acting in the same fashion as the Moon does today. They are also entirely immune to the effect of nuclear bombs, receiving minimal damage upon multiple impacts, simply replying "NOT COOL" in response to General Nathan's nuclear assault. They are able to rapidly teleport entire planets across seemingly infinite expanses of space on a whim, as is shown when they instantly teleport Earth to the set of Planet Music.
Cromulon technology appears to be massively advanced, as they have access to a planet-sized plasma ray gun, capable of annihilating planets in a single shot, which they activate frequently on a whim. As well, they have notably constructed a Dyson Sphere around their nearby sun.
Upon the Cromulons' annexation of Earth, Principal Gene Vagina constructs his own religion - the cult of Headism - in an attempt to please them. Despite the futility of his religion, many of Get Schwifty's events coincide by pure chance with his motives. Ultimately, Earth's population realizes that his religion is nothing more than an attempt to capitalize on the Cromulon invasion, and it is swiftly disbanded at the end of the episode.