I'mma chime in on this one.
Considering how off the rails the expedition has gone, and the hints that they're going to go much further than anyone expected.... my call is:
The... I'm going to call it AE, (Anomalous entity), the AE is actually a someone, particularly a living someone, and quite possibly living in a commune of Christians off in the wilderness of the silent world and we may be about (obviously after a chapter break) to see a clash of cultures take place.
For starters I have (and I think others did too) theorized that a christian community after Y0 would most likely consider mages to be priests/miracle workers.
I'd also say, despite the uncanny valleyness of the face, there's not a lot of evidence of it being a spirit, or at the very least someone from y0-1 (I may end up eating these words next weekend), as we've seen previously the older spirits don't seem to retain their form, or manner of dress over the time.
However, if my theory holds water, the crew may be bringing just about a wall of terror and death in the form of the daisychain of spirits following along.