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Nightmare Fuel: SIREN
Siren/Siren: Blood Curse
"Siren" is quite possibly the creepiest game ever, where out of 10 distinct characters you play as, only the little girl properly survives.
Sightjacking in general. Looking through the eyes of a Shibito gives you not only the ability to see them coming right towards you, but also allows you to hear them talking in their own language...
Even worse: while you're sightjacking, you cannot move. The one thing you do not want to see when you're looking through their eyes is yourself.
The Shibito themselves. In their first form, they look like deranged people, with blood seeping from their eyes. Then they mutate. The first appearance of the dog shibito, spider shibito, winged shibito... Oh, and don't forget the evolved forms of the Onda Twins...
One advert for the game had to be pulled off Japanese TV for being too frightening. The scene in question being Tomoko who having turned into a Shibito ends up screaming for her parents with tears of blood on her face while banging on the window of the church.
There is one boss in the game that you literally cannot beat unless you're prepared to beat it to death with an umbrella.
The music itself is frightening at times.
Only a few characters have access to guns. If you cannot sneak past, or choose to go the action route, you'll need to beat Shibito to death with an umbrella, or a crowbar - that is, if you even have access to a weapon...
More fear is added due to game mechanics; Siren is very vague about what is needed to unlock later levels or to get through the ones you're in. This means you have to go everywhere and check everything - so you have to go into that dark scary shack you don't want to because if you don't, then you might not be able to beat the game. Your map only identifies landmarks which you will need to find; there is no "you are here" marker. Have fun exploring...
In the ps3 remake there is one level in episode 7 with Seigo when you need to help the little girl scape, you're sniping at first and feel very badass, then you go down and need to find an item but as explained before it is vague to find exactly what you want, so if you open a certain closet you find a freaking head out of nowhere screaming and seeing you, I actually checked the same place in other levels and the head is not there, it is a jump scare but a very good one.
Datatsushi. Not so much in the battle against it, but in the cutscene where you first see it alive, it's terrifying. Oh, and in that battle? It's invisible. You have to sightjack it to figure out where it is from the direction you're facing in its view.
During one of the hospital levels, the only way to survive is to hide inside the incinerator.
Siren 2
Yuri Kishida has a face in her chest. A face that smiles.
There's the boss "Otoshigo." It's mercifully difficult to find a still picture, but there's a video of it here. Be warned that it includes spoilers for the final battle against it.
The scene where Mother is first released and the following scenes of the Yamirei arriving. Seeing those terrifying white wriggling things is enough to frighten a lot of people even without Shu Mikami having been swallowed by tentacles during the same scene. On top of this, their defense against the light involves taking over the bodies of Shibito, presumably killing the Shiryo already possessing them.
The smiles on the faces of the Yamibito.
How about the Yamibito that have giant faces?
Other
The advertising. One of the trailers for the first game featured insanely laughing shibito, as well as some gruesome environments and Gross-Up Close-Up used to full effect.
Then a couple of years later, there was the print ad for Siren 2. A close up of a woman's face. With the eyelids sealed shut. That brought back uncomfortable memories of the trailer, as well as being terrifying.
