Dark Tales / Nightmare Fuel

One would expect a series of games based on the work of the horror master himself to have a supply of nightmare fuel. And boy, do they deliver...

The Premature Burial

The whole concept of being buried alive falls into this, in the first instance.
As the game progresses, you learn that somebody has been burying people - specifically, his wives - alive. Later, you and Dupin have to rescue one character from such a fate. Think about it. She was sealed inside a mausoleum full of the dead with no food, no water, and no way to escape...
- It gets worse if you play the bonus chapter of the collector's edition and realize that he's done it three times, all to women he specifically married because their deaths would be easy to fake. You also learn that the sick bastard has a secret tunnel leading to the crypt. Why? So he can listen to each wife screaming and sobbing. That's some top-grade psychopathy right there.
  - Don't forget the fact that there is an accomplice who convinced him to do it in the first place. It's the groundskeeper at said cemetery. He works there, he knows that there are people being buried alive... and he does nothing about it.
  - Why would he? It was his idea!

The entire history of the Usher family is a blend of this and Tear Jerker. Imagine growing up knowing that your fate involves being a living sacrifice to a bloodthirsty house, which has already consumed generations of your ancestors. How old do you think the family members are when they learn about this?
The man in the opening animation is the detective whose diary is found by Dupin. He's killed so his life-force could feed the Usher estate. That's bad enough, but as the game progresses, you learn that he's just the latest in a string of sacrifices to save the last of the Usher line. To judge by the detective's notes regarding missing people, at least one of these was a child!
Arguably worse, in the bonus chapter you learn that the same sentient evil which led the house to demand sacrifices is killing everyone in the village. By the time you reach the very end of the chapter, you and Dupin are the only confirmed survivors (although Speaking With the Dead indicates that Dr. Morris also escaped). Imagine how they must be feeling as they leave all that behind them.

The entire philosophy of the Raven Society falls into this if one thinks about it. This ancient organization went off the rails somewhere along the way and started doing everything in their power to prevent progress, on the grounds that "knowledge need not be shared." Instead of using their widespread influence to make the world better for people, they want to restrict humanity to a permanent Dark Ages where only they have any sort of power or capability. That's bad enough, but then you realize that to achieve this goal, they actively threaten and eliminate people who achieve scientific breakthroughs. According to one of the collectibles, they even targeted Nikola Tesla. Other collectibles indicate that they were responsible for the downfall of the Roman Empire, the destruction of the Aztecs, and even the disappearance of Atlantis.

Morella herself is just a walking bundle of nightmare fuel. She decided she wanted to live forever, and she found the means to do it. But if she wants to stay young while she does it, she has to possess new bodies, and it's implied that doing so binds the souls which actually belong in those stolen bodies to be trapped in her house. And she has absolutely no problem with this. In fact, she seems to enjoy it!

At the beginning of the second act, you find yourself in a prison cell. You and Dupin have been wrongly convicted - without a trial - of committing multiple murders, and are scheduled to be hanged in the town square. All you've done is respond to a call for assistance in a town where murder runs rampant, and your reward is to be hanged as a scapegoat. Obviously this doesn't happen or there wouldn't be much of a game, but it's chilling to imagine.