Demonic Creatures
Demons are a type of Hellspawn being of Chaotic Evil alignment. Their chaotic nature makes them more unpredictable then their lawful associates, Devils. They are susceptible to powers that target Hellspawn, as well as powers that target creatures with the Evil or Chaotic keyword. They are also susceptible to Banishment when not on their home plane.
Demonic Characteristics
Born of Hellfire, Chaos, and Rage, demons are contenders for the most feared and reviled of all monsters on any plane of existence. They primarily dwell within the Abyss, a realm of darkness and chaos that serves as a breeding ground for their wretched kind. Demons come in a variety of sizes, ranging from Tiny to Huge. It is even rumored that in some of the lowest levels of the Abyss, in the lands where not even Demon Princes dare to dwell, are monstrosities the size of castles, beings of pure horror and anger that could devour an entire planet could they only escape. Most demons appear as twisted amalgamations of many mortal creatures, with sinister, warped features. Long, jagged claws and teeth, abnormally elongated limbs, eyes that burn red with an eternal hatred, curved horns, and large leathery bat wings are all common features among demonkind. Demons are hateful, miserable creatures that forever seek to gain access to the higher planes so that they can wreak havoc. In general, demons simply murder, rape, and kill for the fun of it, with no particular goal in mind, and it is only when their power is focused by an outside force that they can intermingle with other planes of existence and cause true chaos.
History
Demons have a long and sordid history filled with acts of murder, betrayal, depravity, and almost every sin imaginable. They are known to cause harm to each other just as much as other races, as they are all ultimately self-serving creatures. They have a particularly volatile past shared with goodly religions and their gods, as their very nature demands that they attempt to disrupt all things holy and lawful. In the past, usually through misguided good intentions and a great deal of misunderstanding and manipulation, Demons have managed to trick their way unto the material plane in great numbers to cause tremendous damage to the world in a very short amount of time. Hellspawn have always been quick to act once released, because demons slain on the material plane are quickly banished back to their miserable home dimension for periods of up to 1,000 years, depending on the laws of the power that summoned them. Still, other demons have been summoned through no act of their own by mortal spellcasters who wish to use their power or knowledge to accomplish a certain goal. Demons, being creatures of pure malevolence, resent being bound to anything and will often try to fulfill their obligation to the summoner in the most twisted way possible, potentially harming or even killing their temporary master while fulfilling their obligation, releasing them from servitude with the added bonus of the material plane being a bit worse than it was before they got there.
Culture
While Demons war with the worlds above them, they also constantly war with each. Much like mortals, Demons have their own factions and legions made up of a variety of their own kind, almost always led by a Demon Prince at the top of the food chain. Much like the rest of demonkind, the goals of these frightfully powerful monsters have no discernible pattern, and theologists speculate that it is this internal chaos and constant infighting that prevents them from rising up as one mass to consume all the humanoid races in short order.
Many uniquely powerful demons constantly seek to ascend through the ranks of the abyssal legions and gain more power through influence. As the fear of their power grows, so too does their strength. Beings such as the Marilith have known a long and curious reproductive cycle that ensures their species dominance in a unique fashion. The Marilith spawns its children, always 13 in number, once every century. Shortly after their birth, they reach maturity, gaining a dramatic increase in power by virtue of their heritage alone. Then, within a day of this milestone, all the Mariliths converge upon the parent demon, and each other, slaughtering one another in a flurry of limbs, swords, hellfire, and martial atrocity. In the end, only one Marilith survives, living for a century as the only one of its kind, powerful beyond measure and feared by all. This is perhaps why, in the rare occasions that the Marilith can be summoned, it always refers to itself and its kind as one in the same. Demons such as these rule entire cities full of lesser demons with an iron fist, and all disobedience is dealt with in death. While all lesser demons fear these kind of Hellspawn, their society and cruel nature demands nothing less than this kind of extreme hostility in what Demons consider a leader.