According to the Dictionnaire Infernal, Nybbas is a demon of hell who manages visions and dreams. He may be associated with the Assyrian and Babylonian god of writing, Nabu.
European Demons: List of Demons in Europe
Many of those classified as European "demons" in this list come from Greek, Roman and Norse mythologies and display trickster-like behavior (e.g. Loki) or are associated with the underworld (e.g. Hecate). Browse through profiles of demons, tricksters and evil spirits from Europe including Greek, Roman, Norse, and Scandinavian demons below. Visit the Demon FAQ for more info on my philosophy behind the classifications.