Moros: Third Moon of Mystara?
by Marc Saindona bit of "fan fic" here, where I associate Matera with Mystara proper, Patera with the Feywild-Good Kingdon (hence all the Cat furries and the moon's invisible nature), and perhaps there is a third moon, related to the realm of Entropy-Shadowfell, a blood red moon, linked to vampirism and the undead. The red moon can at times appear in Mystara as an ill omen, such as moments before an area is swept into Ravenloft. "Moros" could be used as a name until something better is found.
This might serve as a replacement for the Pyts Plane.
Moros.
(Image from: https://www.deviantart.com/kezzrael/art/Blood-Moon-966233333)