Demons are commonly classified through their need to feed off of others. This group has a wide variety of species, but due to their parasitic method of survival, many are hunted or discriminated against. Most species can adapt to the point where no one is harmed and not suffer downsides from it.
While a less mentioned trait, many demons are closely linked to the undead. They can usually see and hear spirits better compared to other classification groups. Many spirits are very open to speaking to demons, so some help spirits pass on.
Some are incapable of producing demonfire. These embers are an excellent catalyst for powerful spells. These are also capable of switching properties. A skilled user can create an inferno without burning anything. Because of the fire having similar properties and color to the flames dragons create, it's theorized that they descended from dragons, but there isn't any evidence that proves this.
Some species are capable of producing a black substance. This is mainly used to give something a physical shape (like emotions and lies). This can happen uncontrollably until they learn how to control it. This can also be a sign of Cordolium.
Most can fall victim to Cordolium (otherwise known as heartache), an illness caused by restrained emotions. This can make them susceptible to curses, being emotionally numb, and constant illness for severe cases. Many who've fallen victim to this produce a inky black substance as their body tries to prevent it from getting worse. The strain will eventually cause their heart to give out from the strain. The best method to cure this ailment is to help them accept the events or to get them caught up in a moment. Those who went through traumatic experiences are more likely to have multiple bouts of this.