Demons
Just as angels are a race of good, demons are a race of evil. They're not sent to this plane by the devil, though they do come from a dimension that can only be called Hell. If you came from there, yeah you'd be evil too after the things you've been through.

Demons go around spreading evil, others through suggestions or acts of major evil. They can curse beings and objects. They're there to make sure that good is crushed. When they cross paths with angel, more often than not, the two will end up in a battle.

Demons can, and sometimes do, breed with humans. The result is a half-demon that is neither full demon nor full human. They have some of the abilities and features of the demon parents but have the option of resisting the evil inside of them.

To walk among the human world, demons have two form. A demon form (their natural form) and a human form they take one. They can switch between the two at will. In demon forms, demons vary from demon to demon. Some have red skin. Some have black. Some have tails, horns, or even wings. Most have fangs and talon like fingers. As humans they're normally attractive, all the better to draw in their victims.

Demons are long lived. They're not immortal but some can live for centuries. They can and do die if mortally wounded. Holy and blessed objects hurt them. They can't cross a line of salt. If the host of a possessing demon dies, the demon dies also.

These evil beings come in many forms and favors. Below are just a few of the different demons in the world.

Succubus and Incubus
These demons are the ones that feed on humans and other beings through sex. During sex they drain energy from their partner and use it to refuel themselves. If they go too long without doing this they grow weak.

Draining someone can't be turned on and off. So even if they have sex with someone for the sake of sex alone, they will take energy from them. Too much sex with the same person can, and will, kill them. Sex with a vampire is the only way around this. Because they are dead beings, they can not feed a succubus or incubus. Supernatural beings give a bigger energy high than humans.

Apollyons
The bringers of disease and plagues. With a touch they can cause any one of the numbers of illnesses out there. They can also take illness away just as easily. Just being around these demons for long periods of time tends to make one feel light headed, sick to their stomach, or develop a headache.

Apollyons tend to work in hospitals and other health care centers were they can cause damage and not draw attention. Some travel town to town causing outbreaks then moving on before being noticed.

Fiends
Fiends are the foot soldiers of the demon world. They have no real abilities other than a super natural strength and speed. They're flesh eaters and will eat any kind they can get a hold of, even other demons. Because they have so little power, fiends are often looked down upon by other demons.

Rakshasas
Another flesh eating demon, these demons have poisoned tipped talons. Just a scratch from theses demons while in demon form can be deadly. They do not have to kill their prey to eat it. The saliva of a Rakshasa demon will rendered their victim paralyzed. Rakshasas must eat flesh or they will die.

These demons hate anything to do with religion of any sort. Priests and church members are often targeted by the Rakshasas to be a next meal.

Pazuzues
The Pazuzu are the demons that possess people. They are the only demon that does not have a form of any kind other than the smoke that travels from one host to the next. Pazuzues can not live but a few hours outside of a host. Because of this they send their demonic life hoping from human body to human body. Some develop a type that they like to possess. It is not possible to possess a supernatural being or another demon.

If a Pazuzu is possessing a human and that human gets killed, the Pazuzu dies with them unless it's a slow death and they have time to escape. If they manage to escape, they come out weak and most possess the nearest human or die.

Daevas
Daevas are the demons of the seven deadly sins. Each daeva specializes in a specific sin. They whisper, influence and push others to comment the sin. With a touch they can plant a suggestion the sin in another, then sit back and watch as it grows. They're the demons that wreck homes and families. The demons that slowly ruin a life. If their target is strong enough they can fight the sin. If the target is all ready prone to that sin, the easier it is to push them toward it.

Daevas not only specialize in a sin, but they in a sense are that sin. Daevas of Lust are usually easy and pretty slutty. Daevas of Pride, well, tend to be full of pride. And so on and so forth.

Bagats
Bagats are shapeshifting demons that can take on the form of other beings. They can become a form they have thought up in their mind or become someone they have seen in person, in a picture, or on tv. When shapeshifting into another actual being there is usually something off. Something they didn't get just right.

Because they take on some many different forms, sometimes even the Bagat forgets what it really looks like. Some lose a sense of self and develop multiple personalities.

Raveners
The destroyers of the demon worlds, Raveners set out to destroy the good in the world more so then most other demons. They make it their job to wipe out the good races in the world, to tip the scales in evils favor. They can sense angels and other beings if their hearts are pure. To help them in their destructive ways, Raveners usually have telekinetic or some other type of psychic power.

Although Raveners have a reputation as mindless killing machines, most are actually quite intelligent and cunning; many actually act with a great deal of subtlety, using betrayal and confusion to destroy as much as they would a weapon. Most of them encourage the violent stereotype to keep the other beings guessing.

Nosthumous
Demons with this ability are able to essentially steal knowledge, memories and personalities of any living creature and retain all of this and are able to use it for their own good. They are also able to impress upon people alternative memories or personalities and also bestow knowledge. Those with less strong will are much easier than those with a stronger mind.

There are degrees to the way they can steal memories, it can be from a couple of minutes to years leaving a person unable to recall what they have done.

Aspects of personality can also be stolen leaving a brave hero a cowardly mouse. However there could be a case where someone very meek is suddenly given a sense of inner strength.

Knowledge can be stolen leaving someone with severely low IQ.
There is also the ability to leave someone an empty husk and take their entire knowledge, memories and personalities. This puts them in to a catatonic state and they will remain so unless the demon returns their thoughts.

Other demons do not know how to react around the Nosthumous. Most are obsessed with learning everything and would not be opposed to stealing knowledge from another demon to do this. They are also invaluable however as they can bestow knowledge on to people, demons included and so help fight good in battles by organizing themselves better and more efficiently.
Nosthumous are arrogant.

They are usually more approachable than most demons however, mainly because they can. They enjoy fine clothes, fine living and believe most (all) creatures are lower than themselves and need their guidance and wisdom, because they are the most intelligent creatures there are.

Nosthumous like to plan and calculate and are highly logical. Before they do anything they must justify the benefit of their actions. Justification is unique to each Nosthumous. Some appreciate balance, others lust for more knowledge. Some for power beyond anything. Others that chaos is the state we started from and must return. Generally loners and usually highly selfish they will take what they want from people and if leaving them a mindless zombie in the process so be it. They probably weren’t using their minds properly anyway.

Nosthumous can look like any demon that is flesh and blood. For instance they could have wings a tail, four arms and a snake neck. But all have horns, little to large, they all have horns. There seemings usually stay fixed for life from the first shape they choose.

Although they don't eat human flesh, they do need to eat raw meat. Raw fish is fine, but not as good as something really bloody and full or iron.

Hell Hounds
Hell Hounds are large, black demonic dogs that have glowing red eyes. Those that have came face to face with a hell hound swear up and down that they could see the fires of hell burning in the eyes of the beast. They are larger and stronger than your average dog. A hell hound can easy break your arm with one bite. Along with being stronger, hell hounds also have some pryokinetic abilities, able to start and control fire.

Hell Hounds can take on a human form like most other demons, but even while in human form, they retain some of their canine personality traits. During a new moon a hell hounds eyes will glow red.

Shtriga
In its true form, a shtriga looks like a decomposed corpse. Despite its appearance, the shtriga displays the strength found in most demons. Instead of feeding on the flesh, the shtriga feeds on the spiritus vitae, the life force of a living being. They drain the life force off of their victim until there is nothing left but a shell left. Most shtriga target children since they have the most life force, but some prefer certain species of supernaturals. The only way to kill a shtriga is with iron while it is feeding.

Asphyx
Asphyx demons are the demons that people are talking about when they say they made a deal with the devil. They are able to summon and manipulate human souls and have the power to grant a person something in return for their soul. When it comes to filling their end of the deal, their power seems limitless. The only time they are able to use such power is when a deal has been struck. Otherwise asphyx demons have little power. The souls that they collect are not ate but instead thrust into a hell dimension where they are tortured.

Ethros
Similar to Pazuzu demons, Ethros demons are demons that possess others. Until like the Pazuzu, Ethros demons can possess supernatural beings and take on a corporeal form. When assuming corporeal form, Ethros demons appear as pale grayish humanoids with large facial wrinkles, yellow eyes and pointed teeth.

Ethros demons can assume an incorporeal form in order to possess humans. The demon can be forced to surface and then exorcised by performing an exorcism.

Once exorcised, Ethros demons will seek out the closest human body to possess, though the force of the expulsion is such that the new host rarely survives. To prevent this, an Ethros Box can be used to attract the demon and keep it trapped.

Ethros demons also possess psychic abilities. They can read the minds of others. Ethros demons are vulnerable when in corporeal form.

Rache
Rache are vengeance demons. They are one of the few species of demons to be created, not born. They are able to grant the wishes of those with vengeance in their hearts. They are created by other Rache who appear to humans who have exacted notable revenge on their loved ones, and transforming them into demons. Rache demons can not reproduce as other demons do.

Rache travel the world exacting vengeance on behalf of victims. Their typical method is to appear to a wronged person and encourage them to vent their spleen about those who have hurt them. The moment the object of the demon's attention expresses their preferred method of punishment in the form of a wish, the vengeance demon can cause his or her wish to come true, whether it requires gruesome dismemberment or even the creation of a new alternate universe. Although vengeance demons' mission in as a whole is to bring forth "destruction and chaos for the pleasure of the Lower Beings", each individual has her own priorities and specialties, such as scorned women or neglected children. Some vengeance demons do not believe their mission is evil at all, and describe themselves instead as "justice" demons, a term which carries less stigma than "vengeance".

Rache can transform into a demonic form, in which their faces appear to be skinless with exposed veins, and possess supernatural strength, teleportation, and accelerated healing. They can sense when people have vengeance in their souls, and can identify whether creatures have souls or not. If a Rache is killed, their wishes can be undone.

Eruorequiro
(colloquially known as Wishmasters) These are your deal makers, and they are usually the demons that practitioners of demonic magic work with. They can grant wishes, but their favors always come with a cost. For a start, there's the superficial cost; Anyone bound in a verbal contract with a wishmaster develops mark somewhere on their body. It looks like a tattoo, but it's actually the demon's brand of ownership, essentially. The brand is specific to the demon, and allows him to find you any time, any where. The brand also burns uncomfortably when it comes into contacts with things like holy symbols or holy water, or the person wearing it is on holy ground. Then there's the fact that you owe the demon a favor in return. They don't always state up front what they want, but they do want something, and usually it results in a helluva lot of destruction. The brand fades once the contract is fulfilled, but the smudge of taint remains on your soul forever.

Eruorequiro can become incorporeal at will, so killing them can be difficult. The hunter needs to either force them to remain corporeal by splashing a potion on them, or trap them, either with a devils trap, or in a container similar to the Ethros box, and then they can be killed ritually with an exorcism rite.

Phobeo
Basically, this is a demon that feeds on fear itself. It preys on peoples phobias, giving people anxiety attacks and night-terrors. Their favorite prey are people who already have phobias or traumatic pasts, which they can use to their advantage. They have limited telepathic ability. They get visions of what people fear, and they can project horrific visions / nightmares onto people. They need to be within a certain physical range to do this. The pay off is better the closer they are to their victim, so often these demons will take jobs in psych wards or as babysitters, professions that allow them to get close to people and prey on their fears.