The fell beasts resemble huge featherless birds with long necks, sharp teeth, and wings formed from a membrane of skin between horned fingers, similar to a bat. The true name of this creature is unknown. They are simply referred to as "fell," meaning dreadful or terrible. The fell beasts may have kinship with Dragon-kind or with prehistoric creatures now vanished from the world. They were likely seduced to evil by Sauron or his master Morgoth and have since been bred as steeds for the Dark Lord's most fearsome servants. After being unhorsed at The Ford of Bruinen, many of the Nazgûl chose to ride these creatures in order to spy from on high and inspire terror.
In Barad Guldur, adventurers must face The Lieutenant of Dol Guldur and his fell beast. Mordirith, the Steward of Angmar, can be seen riding a fell beast in Vol. I of the Epic Quest. Fell beasts also swoop above the heads of adventurers as they travel through Dol Guldur.