An Imp is the starting stage of demons before they warp. For warlocks, imp isn't a stage as much as it is their mature body, as a warlock doesn't warp into a demon. It is unclear but believed that imps have magic but lose it once they warp.
Warping[]
In order for imps to warp, they must undergo feelings of great bloodlust, aggression, war-happy emotions, or hateful excitement. Slime oozes out their every pore and they become cocooned in the substance. Once having entered the warping phase, it may take hours to days inside a sticky cocoon to fully change stages. To help the process, another imp or demon may set the cocoon of a warping imp into a dung pit to speed the transition. This usually happens when imps are 12-14. Once the creature has completed this transition, they are full fledged demons. They also must move out of the imp boarding house and are treated with much more respect by the younger imps than was before.
People and Places[]
In "The Lost Colony", in the demon's Limbo-stuck island, imps are the lowest level of the social chain. If the imp isn't very aggressive or if they don't warp until much later than they others, they could be called an impling. The imp N°1 was called this and is described as an upright miniature rhinoceros with a pure gargoyle head. He never warps because he is, instead, a warlock.