Demons are powerful beings of darkness. In the series, they differ in their forms, sometimes looking like giant frogs while others have three legs, arms and tails. The major demons that were in the Fablehaven Preserve are Bahumat (imprisoned), Graulus (dead), Kurisock (dead) and Olloch (frozen).
Demons vary greatly in appearance. Demons all look like creatures of terror, fear and nightmares and are usually very ugly and fearsome.
Demons of Fablehaven
- Bahumat - Imprisoned, with Muriel, under where the Forgotten Chapel once stood, after Kendra Sorenson led the Fairies in battle to defeat the Demon.
- Graulas - Hibernates in his cave at Fablehaven which also serves as his deathbed. Recently healed by Seth Sorenson using one of the hidden artifacts. He then proceeded to overthrow the Sphinx, and with the help of Nagi Luna, opened the demon prison, Zzyzx. Killed by Seth, using the enchanted sword, Vasilis during the battle against Gorgrog.
- Kurisock - Was eradicated by Kendra with the help of Lena, who sacrificed herself by touching the Corrupted Nail with the Talisman made by the Fairy Queen.
- Navarog - A dark dragon who was so evil he was made a demon prince, and was the prisoner occupying the Quiet Box of Fablehaven until he was released by the Sphinx, and became one of his allies, in form of Gavin. Gavin revealed his true nature in Wyrmroost and met his end in his human form when he was devoured by Raxtus
- Olloch - Immobile until somebody feeds him and restarts the unending hunger. Becomes, once again, immobile when he has digested the one who fed him.
- Lycerna- Reptilian demon wreaking havoc at Rio Branco preserve.
- Gorgrog - Demon king, imprisoned in Zzyzx until, killed by Kendra Sorenson.
- Brogo - Son of Gorgrog, gigantic demon, one of first imprisoned in Zzyzx, was deeply injured due to a light blast from Celebrant.
- Orogoro - Eldest son of Gorgrog, looks mostly like his father, but antlers branch like a moose's, injured by Gilgarol.
- Zorat the Plague man - Tall, thin, humanoid demon pocked with sores, one of first released from Zzyzx, fate unknown.
- Ixyria - Serpentine Demon, a mentor to witches and hags, fate unknown.
- Din Bidor - Wolf-like demon, fear and darkness increase his size, fate unknown.
- Nagi Luna - Elderly, bald, female demon imprisoned in a Quiet Box in Living Mirage, a mentor to the Sphinx who helped him become a shadow charmer and release the demons from Zzyzx , killed by Seth
- Navarog - Demon Prince, Lord of Dragons, one of the most powerful demons, eaten by Raxtus while in human form.
- Jubaya - A humanoid female demon with a head that appears like the charred face of a praying mantis. Jubaya was among the few demons who did not leave Zzyxz when it was opened, and only made herself known when she sensed Kendra Sorenson enter Zzyxz after it was taken over by the Faeries as the new Fairy Realm. She offered to be willfully removed to the new demon prison in exchange for the chance to speak with Kendra. She offers interesting information about the dragons and the names of three other demons, Talizar, Batoosa, and Vez Radim
- Talizar - A cloaked demon with a face like a wolf, glowing red eyes, and rat-like hands and feet. Seth encounters Talizar in a dreamscape called the Path of Dreams, where the demon expresses an interest in Seth for his status as a shadow charmer. He offers to become his new mentor but Seth refuses. Although denied, Talizar simply shrugs it off and tells Seth his offer is still open if he ever changes his mind and if so to seek him in the waking world.