Nobody knows how long it has been in our midst, or what it exactly is. Legends speak of it being as old as mankind itself, but some believe to be immortal, being present since time immemorial. Nobody even knows what it's real name is. 

They just call it The Dark Side.

Of its origins, very little is known. It was first observed by early human beings, when it infected some of their folk. Early on, many tried to understand it, some even going so far as to try to control it.

Needless to say, every single one of them failed.

This entity is very patient. It waits, sometimes even for millennia, for the right opportunity to wreak havoc and destruction. Sometimes, it uses others under its control to create conditions suitable for its passage into this world.

It infests only one mortal at a time, and that too at a slow rate, making its existence even harder to detect. Once it has gained full control over its captive, it speeds up its activities considerably.

This is because the infected cannot survive for long. They decay rapidly, and end up alone in a dark place, where the final push awaits. One that challenges their very existence.

The entity reveals all to its victim. It shows them all their actions thus far, and gloats as it watches their conflict in deciding what to do.

Most of them don't stand a chance. They fall further down the abyss, to never return. Some are able to push back, but end up as pale shadows of their former selves. A rare few are able to muster the courage and determination to get out almost unscathed.

Humans believe that this entity uses the random thoughts that keep flitting through their minds every now and then to gain entry. They feel the only way to keep this horror at bay is to be vigilant at all times.

And to warn the uninitiated, they have coined the saying, "An empty mind is the devil's workshop".