Their numbers are limitless. Their malice infinite. To know them is madness. The Daemons of Chaos are the most feared of foes; they are liars one and all, but it is the truth that damns us above all. They are here because we want them to be. They shall kill us because we deny that want. The Galaxy shall die not in blood and fire, but with a realization: Chaos can not be denied!
I can taste your fear, human. It is a tangible thing. I can run my fingers over it and drink deep of its sticky aroma. If this terror is the food of hatred, let me feast upon it and in the feasting destroy you utterly.
What are we? Your scholars claim we exist only to tempt you, yet in a very real way we are you. We are your own desires, your own fears, your own ambitions and rages, given form (if not flesh). How can you fight us? Only by fighting your own Humanity, and why would you want to do that? You would be fighting against life itself. For what is Chaos but life?
— Tzaal, momentarily lucid Horror of Tzeentch, Warhammer 40,000
Anger, hatred, corruption, become power! Everything that exists will be devoured!
— Sora's Heartless, Kingdom Hearts coded
"It happened when you and I were split into two. The negativity took shape as these monsters. They are what I feel- a horde of fledgling emotions under my control."
— Vanitas, on the Unversed, Kingdom Hearts: Birth by Sleep
While I was out investigating, I found a fascinating new test element. It's never been used for human testing because apparently, contact with it causes heart failure. The literature doesn't mention anything about lump-of-coal-failure though, so you should be fine.
"All they know is how to hurt and destroy and kill. Admirable when you need someone hurt, destroyed or killed, but what about the times when you just want them to sit down and shut up? Oh, FORGET that. 'I wanna go to Earth.' 'I want to kill my old girlfriend.' 'I want to eat my family's flesh and drink their marrow.' 'I want to blow up my school.' 'I want to anally penetrate my kindergarten teacher.'"
"Dementors are among the foulest creatures that walk this earth. They infest the darkest, filthiest places, they glory in decay and despair, they drain peace, hope, and happiness out of the air around them... Get too near a Dementor and every good feeling, every happy memory will be sucked out of you. If it can, the Dementor will feed on you long enough to reduce you to something like itself...soulless and evil. You will be left with nothing but the worst experiences of your life."
— Remus Lupin, Harry Potter
"Understand that there is no point in living! Cry, that there is no answer! Where there is darkness there are shadows! I, myself, am all of you humans!"
"You are me. I am you. I know what's in your heart. Hatred: that's what I really am."
— Dark Naruto, Naruto