Mouse is an enormous, shaggy black dog of indeterminate species.  His claws and teeth are long and slightly fearsome in appearance.  His overall demeanour of doggy good cheer makes him hard to be frightened of.

Oddly, his eyes are a deep emerald green and frequently seem almost to glow even in the absence of an external light source.

Background - The Black Hounds of the Fae are well known throughout the lands of the Celts.  Generally, such beasts are objects of fear and terror for their malign ways.  But such is not true of all such creatures.

One of the exceptions is "The Gurt Dog" of Somerset.  Known for his guidance and protection of travelers as well as his constant vigil over the children of the area, he is a beloved local legend.

Mouse is one of that breed.  In addition to human-level intellect and magically augmented senses, he is a fearsome fighter able to increase his stature to that of a bull's when he or those he protects are threatened.