In Welsh oral tradition, the gwyllgi is a frightful apparition. It appears as a huge mastiff, with a baleful breath and blazing red eyes which shine like fire in the night. One reputedly haunted the lane leading from Mousiad to Lisworney-Crossways, another a field called the Cot Moor, and a third the pit at Pant y Madog near Laugharne, Carmanthenshire. The cwyllgi is reminiscent of the
shaggy mastiff larger than a steed nine winters old which guarded the sheep before the castle of Yspaddaden Pencawr.
All the dead trees and bushes in the plain he burnt with his breath down to the very ground.
- Mabinogion, 230.
- Sikes, W. (1880). British Goblins: Welsh folk-lore, fairy mythology, legends and traditions. London: Sampson Low, pp. 168-173.