Hell, just take a look at the game's cover, and you get a pretty good understanding of what's waiting for you.
The Bad Ending of the game in which you slit Liza's throat and then have sexual intercourse with Citra, who during the session, plunges a knife into your chest, killing you.
What makes this situation worse is that as you are dying, it is very heavily implied that you may have impregnated her and that she will be using and training your child to be the leader of her group. Problem is, she's not exactly sane now, is she?
The beginning of the game. As if Vaas kidnapping and telling Jason that he's hit the ground isn't bad enough, we see Vaas killing Grant and sending his pirates to hunt down Jason in the middle of a dark, hostile jungle. It has to be one of the most intense and horrifying openings in any video game released in the Seventh Generation.
Vaas: I'm gonna give you thirty seconds. And if the jungle doesn't eat you up alive, I will. Are you FUCKING DEAF?!I SAID GET THE FUCK OUT OF HERE, YOU CHICKEN FUCK!!!Run, Forrest, run!!!
And lest we forget, the Ransom ad which features Vaas trying to manipulate Liza for his ransom video.
So there are a ton of pirates and devious folk spread throughout the island. That's not too bad, right? Well, as it turns out, there's all kind of animal life on the island too. Not just wild boar or hunting game animals, but tigers, bears, crocodiles, sharks, komodo dragons and so on and so forth. They can very much sneak attack you and can kill you very quickly if you don't fight back.
And this can also be Nightmare Fuel for the AI enemies. They quite often have caged animals in the vincinity. They're minding their own business, standing guard, when they might hear a whisp of something in the air (your sniping bulliet). They don't know what it is, until suddenly the caged animal (bears, tigers, etc) isn't locked up anymore and is set loose and the AI find themselves being mauled.
You can also often see the animals eat the people they kill.
When animals hunt you, they don't just run up and attack either. They stalk. It's one thing to face down a raging feral dog, but it's another thing to think you hear a bit of movement and turn around to see an entire pack of rabid hounds slinking through the grass toward you. It triggers a primal, instinctive terror to realize that you are being hunted. It's made much worse when you're exploring the islands at night.
The crocodiles are living Jump Scares. One second your walking along a seemingly safe river or standing in a BOAT. The next, you underwater as the croc has you in it's jaws and in a 'death roll'.
Crocodiles don't only try and feast on the player character. You can come across an NPC strolling along the river, the entire scene serene and peaceful, when suddenly a crocodile shoots up, wraps its jaws around the screaming NPC, and drags them underwater. This happens so fast, you can't do a thing but watch.
One sidequest has you heading into a partially flooded cave to investigate the whereabouts of some missing villagers. On your way out, you find out why they went missing.
How about the fucking sharks?? No other animal can sneak up as well as these guys because 1) they make no sound, 2) you can't fucking hear them underwater. At least the other animals grunt and growl if they get close enough. Oh, and there are several relics that are deep underwater in shark-infested waters. Have fun not panicking as you run out of breath and watch out for sharks.
Through the Lost Letters, you eventually learn that the animals of Rook Island are not normal, having been altered in some way by a Japanese WWII experiment to weaponize them called Project Kyouken. Or, in English? Project Mad Dog.
When we finally reach the point in the game where the famous "Definition of Insanity" scene actually takes place things end up rather horrifically for Jason. Vaas shoots Jason and throws him into a pile of corpses. Jason wakes up buried alive under these corpses and has to claw his way out before he is completely smothered to death. When he finally emerges out from under the pile he backs up from the pile of corpses suitably horrified. The thing that saved him from the gunshot? A lighter in his pocket stopped the bullet. Yeah, Jason probably is gonna have nightmares about that one of these days.
One of the rare animals featured in the game, the Undying Bear. In it's side mission you have to go through a dark cave to find it and once you do lay eyes on it, it's a horribly disfigured, rabid-looking animal with chucks ripped out of it, claw marks over its body, and its brain exposed as well as being slightly larger than the other bears you encounter. Oh yeah, and there are some mauled bodies around the area.
There is the gargantuan demon you'll have to face midway through the game. Granted, the boss fight is part of a drug induced fevered dream, but every time you shoot it in the mask with the explosive arrows, you get to see more and more of its horrid, skeletal face.
The really scary part? All of the weird, Maybe Magic, Maybe Mundane stuff you encounter in the game may mean that the demon was real.
Hell, all of the Maybe Magic, Maybe Mundane stuff. The game starts off firmly set in the real world, but things get more fantastic as you go on. Is it all the hallucinogenics Jason has been taking permanently altering his sense of reality? Is there really some otherworldly magic going on? Or is he simply, slowly slipping into complete insanity? The game leaves you with no clear answer and all are equally horrifying.
The fact that Vaas apparently slaughters an entire village just to celebrate his 'killing' of you.
The memory cards are disturbing for a host of other reasons. They're straightforward and matter of fact, discussing acquisition of resources, exploitation of markets, and so on - stuff you'd expect in any corporate boardroom. Except they're talking about manufacturing illegal drugs, with discussion on things like high addiction rates and mortality in a rational, businesslike manner. When you start finding the ones talking about using failed military drugs that cause fatal bleeding being seriously considered for distribution, or date-rape drugs being sent to areas where human trafficking is prevalent, things start getting deeply disturbing.
The fight with Hoyt after you lose your finger you black out. When you come to not only have you killed Hoyt but you killed every guard in the room as well as another six or so guys who must have come in when they heard the commotion. It is hard to claim that Jason is going to fit well back into society after this point
This actually becomes even more horrifying if you look at it from the perspective that Jason intentionally hallucinated that fight to make it more interesting. Given how many dead men are surrounding Jason when the trippy disco light hallucination is over it is likely that Hoyt didn't survive Jason's rampage long enough to gloat and put up a fight. Jason's mind could have hallucinated the prolonged knife fight with Hoyt because the reality of Jason killing Hoyt and several other enemies in such quick succession might have come off as anti-climatic, the death of Hoyt needed to seem more dramatic to be satisfying in Jason's mind. Jason has become such a Blood Knight that ordinary fights are too boring, he needed something to spice things up a bit.
Keith and Riley's fate if you don't save them - sexual slavery. One at the hands of Buck and the other to someone in the Yemen who "likes them young".
Riley's... What, 17?
He's at least early 20's, considering how big a point is made of him getting his pilot's license. Not that that helps matters.
Sometimes, as you pass by the townspeople of Badtown, you can hear them talking in ways that make it clear you aren't the only one going crazy.
The quest "Pinned to Earth" isn't exactly "scary", but still rather creepy. You start the quest by meeting an old lady in a shack, who hysterically reports that a plane crashed in a lagoon a few days ago. You head down there, and you find the wreckage... it's rusted and overgrown with flora. You head to what remains of the cockpit, and you find a man living there. He says that the plane crashed ten years ago, and that it crushed a house and killed the family living in there. When you bring up the old lady, he looks dumbfounded and says that the shack is deserted and no-one lives there. The quest ends, and if you return to the shack, you find it empty, true to the man's word. Just what the hell is going on? Confused old granny, sick prank, or is there something else at work here?
The very end of the fight with Vaas. After stabbing him repeatedly like a crazed serial killer, you fall down next to his dead body, as you see his now dead eyes stare blankly to his left...THEN THEY MOVE.LOOKING.RIGHT.AT.YOU.
You also never see him dead outside of the halucination, unlike Hoyt. The only confirmation of his death is what other characters tell you. So for all you know, that nutcasemight still be alive.
The factbook is almost almost entirely full of humorous entries. But one entry can put some serious Mood Whiplash on that. When on the subject of Patrol Boats, the writer, Agent Willis says nothing helpful or funny about it at all, instead leaving just a sentence about how he sent a patrol out on a boat and none of them returned alive. Its in stark contrast to the rest of the entries.
The one on Seagulls isn't much better, with him ranting about them watching him and suddenly shifting into a flashback of some traumatic event in the jungle.
On the final mission after freeing yourself from your bonds the dragon dagger appears in your hand and you have to make your way across a fiery walkway lined with shadowy warriors with bright yellow eyes. One of them is a shadowy outline of Liza and it steps out and starts to question you in Liza's voice and then dissolves. Not so scary. Then another of the warriors steps out and again in Liza's voice begins to question your actions. That one too dissipates too but then only to pop up at you from the bottom of the screen. Then there's Liza and Daisy standing as tall as giants before a flash of light reveals them to be wearing the mask that the giant you fought earlier was wearing. And they're both staring RIGHT at you.
The red drugs in the basket found in the cave with the "EAT ME" sign. Eating them will give you flashbacks to a nightclub before you got captured. The questions are who put them there, how did they get there and why are they there?
It's pretty obvious that the good Doctor living above the cave put them there - they may even be part of his private stash, but then you have to wonder what he flashes back to.
There's a small house on the southern island which is completely unremarkable on the outside but which contains a bunch of creepy dolls on shelves and hung from clotheslines. Most notably is a dismembered doll on a table, the floor around which is covered in lots and lots of footprints which may or may not consist of dried blood. The house is never mentioned in any quests or by any characters, and no explanation can be found for the house's existence.
There are several rivers and ponds, where if you dive deep enough you can find dead bodies with bricks tied to their ankles, just like what Vaas did to you.