Demons do not exist as an individual species, they are more like a negative expression of the concept of personal anomalies. If a personal anomaly is the full expression of the self in not only a physical sense, but a metaphysical sense as well, then the demon phenomenon is an expression of the parts people would rather bury to that same extent. These first manifest as little whispers in the back of your mind, trying to guide you to perform the steps needed to summon the demon out into the physical world. Feeding into the demon's demands will begin to allow it to touch your body, manifesting as phantom touch. Continuing will then allow the demon to enter your vision, appearing to you as a hallucinatory companion, like a tulpa or an imaginary friend. Once the demon is able to be summoned, its ritual will be revealed to the victim in dreams. The demon will not be unreasonable, those desperate enough to summon a demon can at least haggle so they may get a better pact, after all; nobody can drive a jarder sale on you than yourself. In negotiations with demons, it is important to remember these are not independent beings, they are parts of yourself that have become neglected, if you want to get a good result, you must promise the things the neglected pieces of your psyche would want; perhaps you want to be loved, perhaps you want recognition from your peers, perhaps you want to be surrounded by people who appreciate the things you do, whatever it is, you can leverage it against yourself. Those who aren't willing to make it work will either lose parts of themselves into the devil's grasp forever, or they will become intrinsically linked to the demon's form and function, becoming a beast known as an Inverse-Reverse. Pacts with demons are permanent, even if you heal the trauma creating the demon, its promised effects will persist. A demon can promise you anything, and actually deliver, but you must make sure it is included within the pact, once the pact is sealed, the demon's gifts from the pact are incorporated into your personal anomaly, further specializing it to your needs.