Enoptromancy - The Glantrian Secret Craft centering around Mirror Magic
by Marc Saindon"Magic mirror, on the wall..."
The basic idea is that there is a Mirrorverse of Mystara (not an evil version, but an Ethereal-like plane of existence that binds reality) that initiates can tap into, either for illusions, portals, summonings or bindings of spirits. Divination also work here. The Craft's main cover is involvement in glassware and metal polishing trade.
Notes:
Catoptromancy
(art from: https://www.deviantart.com/janespy/art/Magic-mirror-714166214)