There are always references to Nithian outposts on other planes/planets. Has anyone thought about what those colonies might have evolved into? Here are some of my ideas:
Menkor-Thoth
These are magic users devoted to researching and creating magical beings and monsters. This culture spans several planets in several different crystal spheres. Their system of gateways are still quite active and in good shape, however spelljamming pyramids have fallen out of use.
Each of the colonies/planets is ruled by a separate pharaoh. The Menkothians have grown away from their immortals, and tend to rely solely upon their magic. Each of the pharaohs is a wizard king of immense power. Foremost among the magics of the Menkothians is the craft of Lifeshaping. These are the very same wizards, whose ancestors back on Mystara, created the beastmen, or gnolls. Today several unique species of creatures live with, and serve, the Menkothians.
Menkothian society is based upon a strict caste system, with human wizards being at the top of the list. Next comes the rest of the human population (whose main job is to control the rest of the species in the system). Each of the species created by the Menkothians has a unique place in the caste system, and the culture.
It is rumoured that several elite forces in the Menkothian military have been seen wielding weapons made of a red metal. One of the wizard kings may have found an operating portal that leads back to Mystara, to one of their old colony outposts along what is now called the Savage Coast. He will surely use this to his advantage in his dealings with the other pharaohs. If he discovers the properties of the Red Curse, he may even also try to import it to his home world. The Red Curse, or one aspect of it at least, was developed by the ancient Nithians as a weapon.
Ebor (pronounced Eb-Or)
These clerical orders are most like their progenitor culture. The Eborian culture dominates one entire planet, with several small colonies on different planets. Eborians keep in contact with their colonies in two ways. First, they still heavily use the ancient Nithian practice of spelljamming pyramids. This form of communication is very slow however. The second is by using the Portal system. Eborian Portals are not as powerful as those of their Menkothian cousins. People looking at the Portal can see and hear across to the other side, but can not physically pass through.
Eborian clerics can send their spiritual force across the portals to inhabit the body of a specially prepared mummy (usually a former cleric of their order). In this way, the clergy can maintain a firm hold on their colony states.
It is rumoured that a lone Eborian pyramid ship crashed somewhere on Mystara.
All aboard the ship perished, but a working Portal survived the crash. The
Eborian priests have been trying to make contact with suitable receptacles (mummies)
on the other side of the Portal. If the pyramid crashed anywhere near an ancient
Nithian outpost, the priests may just be able to accomplish their goal.