[[WMG: Rose Madder is Mordred Deschain.]]
Or rather a Twinner to him, on some other level of Franchise/TheDarkTower.
** Can a being like Mordred have a twinner though? There seems to be only one Randall Flagg after all. Also, Rose Madder seems to be on the 'Cosmic Order' side of the alignment spectrum.

[[WMG: Rose Madder is a creature similar to IT.]]
Both tend toward arachnid forms when not needing a less alarming disguise and both have true forms that drive a human viewer insane.
** Which has interesting implications itself, since Rose Madder seems to be more or less on the light side cosmically speaking.