Hagravens are aggressive humanoid creatures with bird-like features. Coming in contact with one can cause brain rot.
They were once witches but gave up their humanity to become hagravens. They despise nature and hunt down spriggans to capture and sacrifice. The Forsworn revere them heavily, and in the book The Madmen of the Reach, it is noted that the hagravens were in the Reach since "the beginning".