VIDEOS:
Abyss Watchers
According to the soul you get for killing them, drinking the blood of the Old Wolf of Farron joined together their souls with that of the Wolf's, implied to be Sif.
Example of:
Merger of Souls
According to the soul you get for killing them, drinking the blood of the Old Wolf of Farron joined together their souls with that of the Wolf's, implied to be Sif.
Example of:
Merger of Souls