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Nightmare Fuel: Knights of the Old Republic
In the first game, the first time you see Malak without his jaw prosthesis.
Korriban In the first game, it's a small world with a Sith academy. The player is required to explore the tombs of dead ancient Sith, which even the powerful Sith at the academy are afraid to enter. In one, you have to have a conversation with the Force-ghost of a long-dead Sith Lord. In another, you're captured by a completely insane psycho who asks you a series of questions, and if you get them wrong he'll torture you with lightning. If you get them right? He'll torture someone else instead. This is added to by the fact that the Sith at the academy are casually cruel, to the point that they'll torture applicants to the academy until they collapse, leave them for dead, and then not even let them into the academy. Nearby, you can explore a cave filled with giant flying reptile things which are more annoying than scary, but also in the cave is a terentatek (think a rancor, but covered in spikes and resistant to Force powers). In one of the tombs, there are two more which you have to fight at the same time. And one of them can kill your entire party if you're not very careful.
The Hrakert Rift station on Manaan in the first game. Full of insane Selkath that try to rip you to pieces inside, surrounded by firaxen sharks that try to rip you apart outside. The outside is actually worse because you can't see them until they're practically right on top of you and your targeting system picks them up. And there are more beyond the edges of the map. Not to mention that you can see the massive one hovering by the bridge, ready to eat you if you try to cross over to the Star Map before you've done something to get rid of it, either by destroying the kolto filters or poisoning the water.
Not to mention the fact that even a scratch from one of them will turn someone into a rakghoul.
The captive Jedi in Malak's command room — dead, but not released to the Force, and serving as battery cells for Malak whenever he needs a Force boost.
Canderous' insight on the unknown planet.
Canderous: This world is... odd. It looks like a battlefield, but the environment is lush and green. Whatever happened here was a long time ago. I've seen many strange worlds in my time and this is the strangest still. (nervously) I don't like this place. Something happened, or will happen, and I don't like it. We should get out of here as soon as possible.
The rakatan computer guarding the Star Map in the Shadowlands on Kashyyyk. All you know about it is that it predates the Republic by 30,000 years and that it approves of dark-side answers. The music doesn't help, and what Jolee has to say about it is somewhat chilling too.
Jolee: Well, well, a Star Map. An ancient artifact of dark side power. Can't say I'm surprised. I always knew there was something funny down here. I wonder if the Star Map has had an effect on the evolution of the creatures here in the Shadowlands. Might explain why it's so dangerous down here.