The gwyllgi (Welsh pronunciation: [ˈɡwɪɬɡi]; compound noun of either gwyllt "wild" or gwyll "twilight" + ci "dog") is a mythical dog from Wales that appears as a frightful apparition of a mastiff or Black Wolf (similar to a Dire wolf) with baleful breath and blazing red eyes.
It is often referred to as "The Dog of Darkness" or "The Black Hound of Destiny", the apparition's favorite haunt being lonely roads at night.
There have been many sighting of this beast in the north east of Wales. Specifically, the Nant y Garth pass located near Llandegla in Denbighshire. It has even been spotted as far away as Marchwiel in Wrexham and as to this day there are still many sightings of this fearsome creature.
- Dogs of Darkness, BBC Wales