Demons

Overview
Hell/Demon dimensions had existed for billions of years, since the very first time the First Evil was able to corrupt a normal soul (The only time it was able to corrupt a Transcendial soul was Lilith) When the First corrupts a normal soul it becomes what is known as a Pure Demon (While not nearly as powerful as a Transcendial they have been around far longer (Due to the first Transcendial soul being less then a Million years old (Lilith)). Some of these pure demons were so powerful that they used their strength to create their own worlds, their own dimensions outside of our own. They then began creating more of their kind (Though these were not nearly as powerful) and would sometimes even wage vicious wars against each other.

Demons were incapable of entering our plane of existence until the first Transcendial who managed to break the dimensional walls into our world from the celestial plane (The Transcendial known as Gaius) and merge with the body of a human. One of the consequences of this act was that it forever weakened the walls surrounding our dimension, allowing creatures from the demon realms to enter our world when they found a weak point (They can also do this through possession of humans, though they are not actually in our world and don't have access to their full powers).

Hundreds of years later when Baskervilles did the same thing as Gaius had done long before him it weakened the walls even more, which is why after Cain gets his powers more and more demons seem to be entering our world that he must fight (Because of how weakened the walls had become after this). Some humans had noticed that Cain had recieved his powers around the same time that more demons started to appear in our world and blamed it on him.. in reality because Baskervilles unintentionally damaged the walls it WAS partially his fault.

Appearance
There are many different species of demon that reside in a variety of different "Hell Dimensions" on a higher plane of existence then that of our own. The number of Hell Dimensions are vast and unknown, and can be created by powerful demons so the number of different worlds has unlimited potential to increase. They can take many different appearances such as Dimensions of Fire, Ice, Darkness, Light, or even those more natural looking such as lush forests. The number of different demonic species that inhabit these worlds is even higher, with many different clans existing in the same world (Which can often cause wars).

Demons have take on all sorts of shapes and sizes. The more powerful/intelligent demons often have weaker or less intelligent demons as their servants or as a source of food. Some Hell Dimensions are ruled by a powerful overseer, while other more chaotic realms have no definate ruler and are home to constant battles.

Pure demons tend to be the most massive and monsterous in appearance.

Powers and Abilities
Each species of Demon have their own unique powers, some a not much stronger then regular humans while others would be considered gods to us.

Some demons lack supernatural strength and instead rely more on physical strength like beasts. Others use dark magical energy to fight. The smarter demons sometimes use the less intelligent (but more phyiscally powerful) demons are protection or warriors.

Some common powers are: Super Strength, Energy Manipulation, Regeneration, Enhanced Senses and Speed.

Demons who live in themed dimensions such as Fire Hells tend to reply on Fire abilities, likewise those who dwell in Ice Hells use cold-based abilities.

Pure Demons are the strongest, usually possessing vast physical strength or higher energy abilities.