
1) English folklore 2) Mythological dog 3) Mythological horse 4) Supernatural legend 
Found on 
https://www.crosswordclues.com/clue/gytrash

 The Gytrash ʃ{cn|date=December 2013}, a legendary black dog known in northern England, was said to haunt lonely roads awaiting travellers. Appearing in the shape of horses, mules, or dogs, the Gytrash haunt solitary ways and lead people astray. They are usually feared, but they can also be benevolent, guiding lost travellers to the right road. In...
Found on 
http://en.wikipedia.org/wiki/Gytrash

In north-eastern English mythology, a Gytrash is a spirit which takes the form of a horse, mule or large dog and haunts solitary ways and sometimes comes upon belated travellers.
Found on 
http://www.probertencyclopaedia.com/browse/DCG.HTM
  No exact match found.