The Worm that Gnaws in the Night, also known as the Doom of Shaggai, is portrayed as an enormous, worm-like entity. It was first observed by the wizard Eibon, who chanced upon it on a journey to the planet of Shaggai.
To his amazement, Eibon discovered that the massive worm was the "Dweller in the Pyramid" mentioned by the demon Pharol, when questioned by Eibon, and that once the Shan of Shaggai made the mistake of summoning it, they could not control or even send it back. Even the Elder Gods could not deal with it.
The worm, to Eibon's horror, was slowly eating away at the vitals of Shaggai and he subsequently made a hasty return to Earth.