The Giant Imp Monster is a one-of-a-kind corporeal entity synthetically created by mistake.
The Giant Imp Monster was created when Peter reversed the polarity of his Proton Pack's stream in an attempt to keep the Imps from continuing to separate into individual entities upon being blasted. After becoming one entity, the Imp Monster went on a rampage. The Ghostbusters lured it to a power plant, where Ray and Egon modified a Proton Pack to draw enough energy to capture the Monster. They succeeded in trapping it but when the Ghostbusters returned, they had to deal with cleaning up the Firehouse, which had been even more destroyed by Janine's battle with The Deadly Three.
Janine and the Ghostbusters refer to it as a demon, and not an Imp.
- Imps have also appeared in the episode "Chicken, He Clucked" and "The Joke's on Ray," but they are different from these Imps.