Metroid/Nightmare Fuel

From the graphic death of Crocomire to the game over screens of Prime and Echoes, the Metroid series sometimes goes beyond the call of scary.

The whole sequence with Crocomire in Super Metroid. Forcing the creature into a pit of lava and watching its skin dissolve. Creepy. Oh, and then its skeleton pops back out for a moment only to crumble before you. Harmless but still freaky.
The Game Over screens of Metroid Prime and Echoes. Oops, you died. For your failure, you must watch poor Samus breathe her last.
- But the point in the game where the metroid breaks out of the glass just after you fight your first metroid is worse, since it happens with pretty much no warning leaving you pretty much jumping out of your skin, even if you're on a second play through and as such are expecting it. And then you get to walk past other metroids trapped in similar apparati afterwards.
  - Not to mention the first metroid itself, if you hadn't played any of the games in the franchise before and only had a vague idea of what they did (from in-game scans).
  - That scene is, by far, the absolute worst the first time around for fans of the original series. Why? Because you quickly realize you're in the worst possible situation: locked in a room. With a metroid. AND NO ICE BEAM.
  - And then there were the Phazon Metroids in the third game. They can let Ice Missiles phase through them. YEEAARRGGHH!
  - The way the metroids grip your face in first-person.
- The Dark Troopers. Right at the beginning, seeing the troopers you've been sent to rescue being turned into freakish automatons and turn their weapons against you. What makes it worse is finding the log books of marines who have either been ambushed or driven insane. One of the freakiest ones was the trooper who got away from the enemies, and as he was heading for the central building sees something in a hole, "Hello... Who's there?.."
  - They'll eat me. Eat.
  - And it's...just...the horrible way they move. The jerky, "puppet with too few strings" motion, more zombie-like than a lot of actual game zombies. Especially when you're just starting out, and this music starts playing...
- Seeing dead marine corpses all over the floors and walls with almost no sign that could confirm how they died is creepy in itself.
  - Such as the ones in the "hive" that drop from the ceiling when you enter this one room! Suspended from their necks like they were HANGED!
- Emperor Ing. What's not to be terrified of? An immensely powerful, mutated Reality Warper far stronger than any other Ing. He's powered by about a quarter of the planet's energy, can regenerate by leeching off said energy, and can take many different forms. Some of his attacks are almost impossible to dodge, and he's only capable of being hurt under specific circumstances.
- Corruption adds the GFS Valhalla, complete with logs of the Aurora unit slowly being corrupted with Phazon.
  - To add to the effect, after a certain point bright flashes near you allow you to see your own Phazon-corrupted face. Considering that at that point you've already seen what the stuff does to Space Pirates and your fellow bounty hunters, you might be a bit more careful with the Hyper Mode. Not that it matters, of course.
  - Then there's the part where you open a door, everything's fine everything's good. Then the second you open the door a dead pirate's corpse greets you and instantly decomposes!
  - Particularly freaky is when, in the Valhalla, you see a Metroid floating lazily down a hall...and then you notice that it's dragging a corpse behind it.
  - You can use the scan visor on corpses to determine how they died. While you can do that in multiple places, the death messages are creepiest in the Valhalla. I distinctly remember one of them saying that the trooper was trying to crawl towards the exit before being attacked from behind, but there are probably far worse "gems".
    - Some deaths include getting impaled with a scythe before being tossed into exploding canisters, a PED malfunction eating a Trooper alive, phazon grenades, explosive decompression due to broken visor, friendly fire while trying to remove Metroids, self inflicted wounds while trying to remove Metroids, and getting attacked through walls by phase shifting Metroids.
  - Phazon Mines! WHY, RETRO?! WHY?! Even with the Phazon Suit, it's scary to step in phazon. IT CRACKLES! CRACKLES! AND IT'S NOT JUST THE GEIGER COUNTER GOING OFF!
  - Of course it crackles. It's laughing at you.
  - Whatever you do, don't look out the window of Valhalla; that entire nebula out there? Metroids as far as the eye can see, some of them MASSIVE.
The SA-X from Fusion. Not only are you powerless to defeat it throughout 95% or the game, but it relentlessly pursues you when you're in its sight. Heck, just the sound of its footsteps as it approaches--and the Leitmotif that accompanies it--is scary enough.
- The worst is when you're cowering in a corridor somewhere, listening to TAP TAP TAP and praying that it doesn't turn into that loud, fast paced track, because that means it sees you. The SA-X encounters are some of the most terrifying things in the entire Metroid series.
Just the X-Parasites in general. A normal human being would have no protection against them at all, and you wouldn't even know if anyone or anything was infected until it was too late.
Other M has some good scares, but the best one is retroactive. Throughout the game, you've been encountering distinctive Power Bomb doors; you've probably been looking forward to coming back and opening them all. Then the cinema before the final fight reveals that those aren't doors -- they're dormant insectoid cyborgs strong enough to kick your ass. Next time you play, good luck passing one without shuddering...
Another one from Other M: At one point, you're running through a big glass tube thing. Suddenly midway through, the game goes all Matrix-y and a giant worm monster attacks, shattering the section of tube you're in. You're supposed to dodge the thing to survive, but on the first run through, it scared the crap out of me.
What about Other M's reshowing of Mother Brain's One-Winged Angel form? She was scary enough in 2D!
In Corruption, you're going to go get the Seeker Missile. As you do, you pass by several trapped metroids. But they do nothing, as they are properly contained. Then you acquire the Seeker Missile, the lights go out, and you KNOW what's waiting for you on the way back. And if it's your first run, PRAY!
As if Metroids weren't scary enough already, this picture makes them look like halfway realistic animals... and the accompanying description of death by Metroid will make your skin crawl.
Metroid Fusion is a lesson in High Octane Nightmare Fuel, and the scares don't stop at the SA-X encounters. Some enemies or events will catch you completely by surprise. After getting the Ice Missile in Sector 5 (ARC), on the last two rooms before the Navigation Room, alarms start screaming, the screen flashes red and the intercom announces "Emergency in Sector 3." After finding out that the main boiler would explode in six minutes, this troper's heart raced while the countdown ticked away.
- And a few rooms before that there's the shadow of a large creature flying around in the background. Later on, when you meet the creature (appropriately named The Nightmare), it becomes scary for a different reason.
- ARC is also where you first end up fleeing the SA-X. Apparently the reason you shiver in Sector 5 isn't because it's cold in there but because it's a Nightmare Fuel Station (attended by a gravity altering robot-zombie named The Nightmare).
- When Samus's computer C.O. requests her to head back to her ship after saving Sector 3, there's a sudden power failure while on the Main Elevator. Everything that happened between the power failure and the power restoration kept this troper on his toes.
- Neo, freaking, Ridley. Before you fight him, you find a weird Ridley-shaped cocoon thing. Walk up to it, its eyes open, and then it mutates into an even more montrous version of the dreaded Space Pirate Dragon. And his screech...
- The music from Fusion. It's like the soundtracks from Super Metroid and Silent Hill got thrown into a blender. A good two-thirds of it is very subdued, tense, and ominous.
The Grenchlers from Echoes. The roars and appearance, they can swim AND jump really high and far which means there is pretty much no way to avoid them...
- Quite possibly the scariest part of the game, The Dark Grenchler. OH DEAR GOD, THE DARK GRENCHLER! That thing still terrifies this troper to this day.
Dark Aether, a nightmarish version of the planet Aether in which you quickly lose energy when not standing in a light-provided safe zone. The enemies in Dark Aether are even tougher versions of their normal world counterparts.
After Gandrayda is defeated, she goes through a Shapeshifter Swan Song, finally settling on Samus' form. As Dark Samus appears to absorb her the way she did the last two bounty hunters, Samus knows there's nothing she can do to help Gandrayda, and essentially goes through the epic mindfuck of watching herself die horribly.
There's a reason the Aazelion, a creature found in Corruption on Phaaze, is this page's picture.
The injuries many of the Space Pirates have suffered in the beginning of Metroid Prime are downright gruesome, and scans even show images of their injuries. Two of the worst ones happen to be one whose exoskeleton's joints were fused together by acid, leaving him unable to move, and another pirate who died by having his internal organs eaten while still alive.