Rhygenta was originally created by Eclipse the Darkling as the future and stronger generation of the Black Arms. While still an egg-incased larvae, Rhygenta and its kind were taken to Sonic's World onboard New Black Comet so they could feed on and grow stronger on the local life. When the New Black Comet was about to be obliterated by Team Dark and the Spider Troupe however, Rhygenta and the Dark Arms' eggs were loaded onto an escape shuttle with Eclipse and send down to Sonic's World so the remainder of the Black Arms race could avoid extinction.
The shuttle eventually crashed in the Red Mountain Zone on Angel Island, where Rhygenta was one of the few Dark Arms surviving the landing, along with Blurk, Cregal, and Cyzer. After being found, Rhygenta was tamed and raised by Eclipse, who swore vengeance at Shadow for killing the Black Arms and Dark Arms. Following some days of nurturing, Eclipse left Rhygenta and the others to find a better source of power to make the Dark Arms stronger.
Rhygenta is a small Dark Arms hatchling whose body resembles a eighth note with two thin feet on its bottom. It has black skin, a single magenta eye with a thin pupil, and a magenta-glowing mouth.
Rhygenta, unlike the other Dark Arms, is good, well-behaved and friendly, making it easy to feed. However, Eclipse speculates it would not be the strongest of the hatchlings.
- Rhygenta's name is a portmanteau of its appearance shape, "rhythm", and its secondary color, "magenta".
- Rhygenta's design, like most Dark Arms hatchlings, is reminiscent to one of the Wisps, specifically the Magenta Wisp.