It is my observation that they seem to blend humanity with the beasts of the land. Some appear as cunning predators, while others embody their role as seductive temptresses, but all reflect a perverse imitation of life. Interestingly, most demons take on the forms of women. I have theorized this is not coincidental: the Goddesses, in their hubris, allowed for the female form to become worshipped as reflections of their own image. Thus it stands to reason that demons--a dark reflection of the goddesses creations, would take on feminine bodies to achieve the inverted power structure we see today. Humanity's own myths tell us that men were created as a counterpart to women as their partners, which is likely why men so often fall prey to demons.
This brings me to the crux of my study: the magic of demons. It is both peculiar and potent, rooted in their nature as spirits and their eternal mandate from the Goddess of Corruption herself--to spread sin. Unlike the orderly systems of elven magic, demon magic operates on the whims of desire and intent. It is a magic of bargains, of granting wishes. Yet this is no benevolent act. Demon magic thrives on twisting the desires of mortals, and seemingly solely exists for this purpose: to distort the intentions of mankind into something foul and abhorrent.
For example, should a human man wish for wealth, a demon might enflame their ambition and inner ruthlessness, allowing them to claim the wealth of others through violence. A similarly vague wish, such as asking for power, could result in the man transformed into a tyrant in a matter of years, only to become hated and eventually slain by his own subjects. The wish is granted, yes, but the path to fulfilling it will always be steeped in sin, which fuels the demon's magic.
The source of this power is sin itself--a corruptive force that grows over time, feeding a demon's strength. However, it is a double-edged sword. A demon's magic is exceptionally weak when used for their own personal gain, to the point where it could be considered benign. Sin desires to be spread to mortals, thus there is a limit to what a demon can achieve alone. Yet, when a demon acts on behalf of a mortal, or even if a mortal were to unwittingly benefit from their actions, their power is amplified manyfold. This becomes especially potent when directly granting the wish of a mortal, especially wishes that are rooted in greed, lust or envy.
Side Note: Demon magic, when tied to long-term wishes, often manifests as a "demon's mark," a lingering tether that binds the mortal's soul to the demon. It's not atypical for mortals to seek out demons for these marks, as they are known to grant boons, such as improved vitality or strength beyond human capability. These marks often allow the demon to track their charge and ensure the wish fulfills their agenda, often spreading sin in subtle ways. While some mortals live and die without facing repercussions, their marked souls inevitably return to the demon, becoming their possession. Such bonds, though seemingly fortunate, are almost always a trap.