Telescopic view of Omen's satellite Rival, as seen during the peak of the Omen apparition.
Rival is the most distant Ominous Planet. It's named Rival since, during Omen apparitions, its brightness and ruddy color rivals that of the brilliant red giant star Rodocer*. It's smaller than Oldsky and Gymnome, but its apparently rocky composition indicates it's most likely a captured Primary Planet like Oldsky, although it does orbit prograde. The gentle capture of not just one but two major primary planets raises questions about whether Rival really is a captured satellite, or if it was formed around Omen and somehow survived the capture of Oldsky. Rival appears to be a dry desert planet with a very thin atmosphere, but glints of sunlight reflecting off of dark flat regions indicate that some of its craters might have liquid water.
*this is continuity with KSP mod whirligig world. In the 'real' mellanus/gymnome worldbuilding, the star is probably called something else!
up-close shots: (spoilers for the mod!)