Freybug is a monstrous Black Dog that is stated to come from medieval English folklore, specifically from Norfolk.
Like most supernatural black dogs, it was roughly the size of a calf, and wandered country roads terrifying travelers.
The English martyr Laurence Saunders mentioned Fray-bugs in his letters to his wife in 1555.
Popular Antiquities of Great Britain, by John Brand, referenced Saunders' letters and suggested that the Fray-bug was a Black Dog similar to the Barghest.
[2] Carol Rose seems to have drawn on Brand’s work for her description of the Freybug.