Demonic Creatures

When the universe was created, chaotic energies form a realm known as the Twisted Nether. Light and Void bled into the realm turning it into a realm of extreme chaos. The result of these two energies merging together was demons. The Twisted Nether is home to dozens of demonic beings who seek to destroy life and devour the energies of the living universe. Eventually the demons discovered ways to travel into the physical universe.
In order for a mortal being to be transformed into a corrupted creature or demon they must be infused with the Fel Energy, which burns away life to create evil magics. Willing or not, creatures can be transformed into demons. The transformation is very altering, leaving little to nothing of that creature from before. Demons spirits/souls are bounded to the twisted nether, when demons are killed they are sent to twisted nether and await for some time to be born into new bodies, with all previous knowledge. Demon cannot be truly killed unless it is imprisoned or banish with some type of high level magics or light seals. It also been known that some powerful demons that have been slain did not require seals and did not return, it is unknown why this happens.
A demon will always, ALWAYS, /ALWAYS/, feed on life and magics, their hunger cannot be sated for so long. Demons have many ways of manipulating the mortal world into feeding their hungers and thirst for chaos. Each demon works different in their own way, some just murdering, some manipulating, some raising armies, there is many ways of evil.