Storms over Seawatch
The librarian's shadow... literally.
This wraith appears to be part of the Librarian’s shadow until she orders it to separate from herself. The spirit seems to be quite literal-minded, obeying the Librarian’s orders to the letter, but displaying no real intelligence of its own.
It appears as the black silhouette of a robed humanoid, swallowing all light and detail that might give clues as to its nature beyond that.