Secrets of Mystara
The Magi worship the god Usamigares. They control at least three rooms on the third level of the pyramid, including a food storeroom, a temple, and a dormatory. They are mixed men and women and wear rainbow-colored robes and silver masks. They appear to all have been arcane casters.
They captured the party but freed them in return for the party convincing the Warrior Maidens to leave the pyramid.
Their leader in the pyramid is Master Auriga. In the undercity, they seem to have either a consensus or some sort of council of governance. The “gatekeeper” is Alyria.
In the undercity they live in the Complex of the Magi, which is a single large, low building surrounded by a low stone wall. The wall does not have doors, gates, or windows and possibly can only be passed magically.
The Magi have said that their study of astrology indicates that the planets are currently favoring a time of great change, with both union and dissolution taking place. They do not have anything specific to say about the party’s roll in these events.