Galleytrot

The Galleytrot was a ghost dog, something that chased travelers on lonely roads and haunted lonely places. A white shaggy dog, difficult to spot, it was said to cause fear amongst men.

In A Shiver of Light, when the unaltered black faerie dogs presented themselves to Meredith's children, one which approached Gwenwyfar was altered to a galleytrot at her touch. It had huge saucer like eyes, and great jaws of razor sharp teeth.

The only other galleytrot that came through the wild magic went to the goblin/sidhe twins Holly and Ash.