"The Innkeeper"

This mysterious figure features heavily in the history of The Old Fort, but there are no depictions of her to be found anywhere and Kethsalen and Mira have only encountered her as a disembodied presence so far. It is known that she is directly responsible for the death of both Lord Rollin Glimmerguard and his wife Onyeka by means of magic and she is suspected in the disappearance of a large number of villagers and travelers over the decades. 
Kethsalen and Mira encountered The Innkeeper when they engaged a ghoul feasting on a lizardfolk cadaver in The Bell and Candle Inn. As she was invisible or etheric at the time they detected her but never actually saw her before she left the building. On further investigation of the Inn they found an attic stuffed with humanoid bones and horrifying active magical glyphs on the walls of what they assume is her room featuring various bodily fluids and other thankfully unidentifiable ichors. Mira used magic to try and identify what she was looking at and found snippets of Abyssal, Infernal and Primordial within the incantations. 


While not undead, Night Hags are known to Kethsalen and he suspects they have stumbled into the lair of one of these very dangerous fiends. The history and particularly the downfall of the settlement and fort fits the profile of Night Hag meddling and the hints gleaned from her magic sigils corroborates that conclusion.