Nightmares

Nightmares are midnight-black horses with burning eyes and hooves.

Sightings of Nighmares are rather rare. The largest number of them seen in any one place are the keep of Rabindrinath in the Dream Realm, where they are all hostile and he keeps a couple in his stables.

The only sight of one in the waking world are in the Mountains of Freedom, where one is kept as a pet (possibly by the mad sorcerer Lorthondo). The nightmare is described as a 'treasure and daemon in one,' and also as male (indicating not all nightmares are mares or the writer of that particular letter knows nothing of equine anatomy).