They look like dogs but are stronger and faster than mortal dogs and they don't feel pain. The Black Court uses them to make up for the weakness of the Renfields and the thralls that don't make good sentries. They make it difficult for attackers to get past—they'd have to be: invisible, inaudible, and unsmellable.
In the seriesEdit
In Blood Rites, Harry Dresden, Karrin Murphy, Jared Kincaid and Ebenezar McCoy go up against Mavra and her Renfields and their darkhounds with intent to kill Mavra and her nest. They get ambushed while trying ot free captives.