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Nightmare Fuel: OFF
OFF would not be as disturbing as it is without the incredible soundtrack. A good example of this is during the 'endless hallway' in Zone 3, especially during battles. Then, of course, there is the music that plays when you return to purified zones. Truly chilling stuff.
Also from the Zone 3 hallways: how about narrowly escaping the Advancing Boss of Doom only to turn a corner and find EVERYTHING'S GONE WHITE! AND THE MUSIC'S BEEN REPLACED BY DEMONIC WHISPERING! For added effect, try stumbling into this while playing late at night!
The fact that the game doesn't even explain what happened to the hallway makes it much more disturbing.
Zone 3 is horrifying in general. The cutesy ghosts that you've been fighting all game are shown murdering an Elsen in cold blood, the relaxed Elsens in this zone are revealed to be addicted to "sugar" and go Ax-Crazy if they don't eat it, it turns out to be made of dead bodies, the music is suddenly replaced by a horrifying remix of the normal battle theme..
Fighting a Burnt Elsen for the first time after discovering the truth about sugar is perhaps one of the most potent jump scares in the game.
It's not just his appearence but the fact that he barely fights you at all and you are forced to kill him. Even trying to run away from the fight, the Batter will refuse.
After beating the first Zone, you're probably be wondering what'll happen if you head back. The entire world has turned gray, with no NPC in sight. The background music gets replaced by ominous music filled with whispering and sometimes the noise of someone slamming their fists frantically accompanied by muffled cries. The enemies are also replaced by demonic dolls, and the music continues playing during the battles. How unsettling.
Enoch's giant head lying in a pool of blood after you kill him is creepy. ESPECIALLY WHEN HE STILL TALKS TO YOU.
There's also the Jump Scare he gives you when you arrive at the tram station. You're just walking around, looking for something to do about this huge guy who you simply couldn't hurt, and just as you enter the room, he comes bursting out of the floor, even bigger than before, and pissed off.
In the final battle, if you go with the Judge's ending, you're forced to fight the Batter. After the screen transition, you see that the Batter turned into a hulking monster out of nowhere. The horrifying part is wondering whether he just transformed, or if he was always like thisthrough the whole game.
The "fight" with Hugo is extremely unnerving. After all you are helping the Batter kill a small child who might even seem to be the Batter's son, and who doesn't even fight back.
The other "fight" with the sugar-deprived Burnt in Zone 3, who does nothing but cry out for help is pretty unnerving as well.
To make the second "fight" worse, it's implied that the Zone 3 Burnt was either only partly Burnt, or not Burnt at all. In other words, it's possible the Batter just killed a defenseless Elsen who was just calling for help.
The noise the sugar-deprived Elsens in Zone 3 make.
After you finish your fight with Japhet, you're treated to the game's first example of Cerebus Syndrome in the works: instead of Japhet's body simply disappearing like Dedan's did, you're treated to a sprite of Japhet's mangled body lying at the Batter's feet, blood and feathers scattered everywhere.
Not to mention the fate of the Judge's brother, Valerie. He attempted to eat Japhet, but didn't chew enough...so Japhet controls him from the inside, and proceeds to horrifically burst out of his body for the boss fight, with Valerie's empty body hanging around his neck.
Who told the Batter what to do all along his journey? You did. Who solved all the puzzles? You did. Who made the Batter kill the Queen and Hugo? You did. In the official ending, who chose to side with the Batter and help him finish what he began? You did. Who chose to pull the final switch and end all existence? You did.