Grimhounds

Grimhounds are the terrible hunting mastiffs belonging to the Queen of the Elves. They are thought to have originated in a different part of the Multiverse and to have strayed into her domain, only to be trapped and subjugated by her. Taking the form of huge red-eyed mastiffs with lethal metal teeth, they are normally deadly to any running creature the Queen sends them against. But the mousepipes of a NacMacFeegle Gonnagle exploit one of the weaknesses universal (or perhaps Multiversal) to all canines. Operating at an ultra-high frequency, the Mousepipes act like a dog-whistle to them and are excruciatingly painful to their ears.

Annotation

There are copious references to Otherworld dogs in Roundworld mythology and fantasy writings. The Wild Hunt of English mythology, in which Odin/Wayland rides the skies at night to hunt whatever he can find, have the God accompanied by terrible red-eyed black mastiffs. These also appear independently in Eastern England as Black Shuck, the massive hell-hound, always black with glowing red eyes. (Dog, in Good Omens, is originally such a hell-hound until reshaped by Adam). In literature, this is the form Bram Stoker's Dracula takes when he arrives in England, at Whitby, Yorkshire. (As would be known to the H.P. Lovecraft Holiday Fun Club, who certainly know Whitby). In Michael Moorcock's second Corum trilogy (based closely on Irish mythology) Corum is beset by the Hounds of the FhoiMyore, who are also vulnerable to the sound of music their ears and minds cannot stand. And in O'Shea's The hounds of the Morrigan - a fantasy adventure Terry Pratchett has homaged elsewhere in the Discworld - they are the eponymous Hounds, serving the war-and-chaos Goddess who is poised to recapture modern Ireland.