Powerful engines of destruction, fiends are beings that differ from nature because they operate against its balance. Fiendish is also a term used to denote any creature or thing which is tainted by dark magic.
Peculiarly, these beings are not dull like animals are, and they even have names. More interestingly yet, they exclusively communicate through telepathy, even capable of causing madness and psychosis in those to whom they speak. Telepathic contact with a fiend is characterized by a high level of pain, physical and emotional, concentrating in the head like a severe and disorienting ache.
Their lineage dates back further then humankind, and the what breeds them is unknown. The only thing known about their origin is that they are born in the deepest shadows; a cryptic message passed down from the earliest humans.
"They art not born, but excreted; lo, for the strongest of the litter devours the rest, and their tails grow from his spine thereafter, and his might will amount to theirs combined. He rises quickly in scale, and sets his eyes upon all that is of the light, in hunger."
Some of them roam the countryside, causing chaos and tragedy before quickly disappearing into the wild. Others are passive; guarding abandoned and long untrodden places keeping the peace that their fiendish rot may fester in shadow for all time.