In fungology a demon is a spirit that has been corrupted by some means. There are two main types of demons: Imprints and Shifters. An imprint is a demon that is pressing its soul (or souls) against a weakened dimensional wall, impressing its soul or, depending on the weakness of the dimensional wall, physical form into another dimension. Imprints tend to be weaker demons. A shifter is a more powerful demon or group of demons that either find a dimensional hole or create one using a ritual and then travel through it, their physical forms entering a new dimension. Demons can be killed using certain rites or weapons and parts of them can then be used for spellweaving or alchemy. Arguably Shifter demons, although more powerful are easier to kill as their physical forms can be destroyed thereby preventing them from coming back, whilst Imprints are shielded by the dimensional wall to some extent and cannot be fully killed, just greatly weakened and temporarily stopped from reappearing. Certain wards and charms can also be used to prevent demons from entering a space but each time they try the charm/ward will be weakened until it breaks.
A dark demon is a demon that has taken a mancer's distortion after killing them and absorbed their dimensional tears into itself. The tears will endlessly fuel the demon with dark energy allowing it to grow and grow, potentially reaching its God State.