Nybbas
Nybbas is a demon.

Dictionnaire Infernal 
Nybbas, is a demon or spirit in the Dictionnaire Infernal, that manages visions and dreams.
He is regarded as a buffoon and a charlatan.  He is depicted as smiling.  He is of the inferior order, high upper gallery of hell.

Similarity with Nebahaz 
The name Nybbas resembles "Nebahaz", one of several deities protecting the individual cities of Samaria who are mentioned specifically by name in the Bible, in 2 Kings 17:31. In his "Encyclopédie Théologique", or "Dictionnaire ... de la Bible", Augustin Calmet asserts that Nebahaz and Nebachas are one and the same and associates them with Nebo, another name for the god Nabu.

In Nomine 
In the In Nomine RPG, Nybbas is the Demon Prince of Media.

Resources 
 Dictionnaire de la Bible, by Augustin Calmet, in Google Books
 Dictionnaire Infernal, by Collin de Plancy at Delirium's Realm

Demons