Gabriel Rachets are also known as the hounds of the hunt, or in more modern times, as hell-hounds. These sleek, black fey dogs make a bell like sound when howling.
Two of Doyle's aunts are Gabriel Rachets and Doyle is able to shapeshift into one of these hounds.
In Mistral's Kiss a group of Gabriel Ratchets were milling around Doyle after the fight with the wild hunt.