- The fact that because the X parasites can obtain the knowledge of their victims, they can potentially build spaceships and infect the whole galaxy at an exponential rate. Yikes.
- X themselves are pretty much straight transplants of the creature from The Thing (1982). The game is not shy about this particular piece of influence.
- Also, the SA-X's face. Need to say more?
The SA-X. An enemy with my strongest abilities. But does it have reason? Probably not. It's just a killing machine. In my current state, I can't face it head-on. The SA-X is me, only heartless. I must stop it before it learns its potential and threatens the universe...
- SA-X IS Nightmare Fuel itself. It mimics a full-power Samus, can kill her easily, and the theme for when SA-X is around is... unsettling, to say the least. It speaks volumes when Samus even lampshades it herself when discussing it —
- The sound of its footsteps invoke the worst kind of terror. This thing can, and will, kill you easily. The only way to survive is to run for your life.
- If you play Metroid Fusion enough, you can hear SA-X coming just by listening to the theme. Its presence invades your subconscious.
- Late into the game, the SA-X is found in the restricted laboratory area, fighting off larval Metroids and thankfully not paying attention to you. However, this causes a self-destruct sequence that will detach the restricted area from the rest of the research station and make it explode. Once you haul ass out of there, you'll likely be delighted to know that the SA-X didn't follow, and exploded with the rest of the restricted area. What you certainly won't be delighted to hear, however, is that the SA-X had asexually reproduced, and now there are no less than ten of them on the station. You know, because one of the bastards wasn't bad enough! Thank god that this ends up being a case of Gameplay and Story Segregation, and you won't encounter any of them until you fight the SA-X as a boss later on, otherwise a lot of people wouldn't be able to finish the game from sheer fright alone...
- Speaking of said fight, when you battle the SA-X as the penultimate boss, it does not disappoint- dishing out attacks just like yours and flying through the air with horizontal Screw Attacks. When you take out enough of its health, the SA-X falls to one knee and it looks like it might be over. Then it turns into something that Lovecraft would've been proud to come up with.
- Nightmare, Nightmare, Nightmare. While the SA-X might hold the reputation as Fusion's scariest foe, if not in the whole franchise, Nightmare comes a pretty close second. This... thing is a massive, mechanical, floating monstrosity that can alter gravity at will thanks to the manipulator on its underside. Just look at it◊! Even the music that plays while fighting it is unsettling.
- Think that it's not scary enough? As you fight it, its "face" begins to leak a green fluid from its eyeholes, in a way that makes it look like it's crying. Keep blasting at its face, and it will explode... revealing Nightmare's true face◊ underneath. Good fucking lord.
- Did we mention that this thing was created by the Galactic Federation - i.e, the guys on your side (or at least the guys that were before you find out their motives)? The fact that the "good guys" have this thing and not the bad guys is pretty unsettling.
- Made by the Galactic Federation or not, just consider for a bit why Nightmare was even created - It was made as a military weapon. Just imagine, you're fighting the Federation, and they suddenly unleash this ungodly monster that immediately begins increasing gravity, making it impossible to move, and ripping your fellow soldiers apart with ease (all while "crying" green ooze), and when it comes for you, the last thing you see before you die is that goddamn face. Have fun with that thought when you go to sleep tonight.
- Nightmare also gets much more of an introduction than most of the other bosses, giving the player sufficient time to build up their own unease. During Samus's first trip to Sector 5, the player enters an enormous windowed room near the start of the Sector and every few seconds a huge silhouette flies past, causing the entire room to shake every time it does so (which you just know you're going to wind up face-to-face with eventually). Much later in the game, there's an explosion in Sector 5 and when Samus goes to investigate, all the windows in the room are shattered and Nightmare is nowhere to be found.
- The Galactic Federation's motives. They denied Samus from blowing up the space station so they could capture a live specimen of SA-X to use as a controlled biological weapon, despite the 100% risk of it killing them all, then raising them as mutant zombies, and then multiplying, spreading across the galaxy, eventually the universe, destroying all civilization. The Umbrella Corporation has nothing on these guys.
- Pretty much the entire sequence after the power goes out. It's a perfect example of Nothing Is Scarier, and you expect the SA-X to show up at any moment while you're stumbling around in the dark. Thankfully, it doesn't.
- Considering how much your AI companion holds your hand through the first ~2/3 of the game, it's actually quite unsettling when you start doing in-universe Sequence Breaking that leaves him surprised. Shortly after the aforementioned power outage, it suddenly becomes very clear that you have entirely jumped the rails; the sense of exposure that realization grants is surprisingly jarring.
- EMERGENCY IN SECTOR 3! EMERGENCY IN SECTOR 3!
- Serris, the boss of Sector 4, can be pretty scary all on its own, basically being a super-fast water snake-dragon-centipede thing. Seeing what happened to the real Serris is just plain unsettling, though. You're informed by Adam that Serris is contained in a breeding tank located just before the actual boss room. "Environmental Disquiet" starts as soon as you enter the room and you see that Serris, this big nasty monster that Adam warned you about, has been reduced to nothing more than the skeleton now lying at the bottom of the tank.
- At the very beginning of the game, you can enter a cold storage room where you can see the frozen remains of none other than Ridley. After the power goes out, you have to pass through this room again and come face-to-face with the long-dead monster. Then he crumbles into pieces as a Core-X floats away, having stolen Ridley's DNA. Then, almost at the very end of the game, you find Ridley again at the bottom of a tall room, only now he looks like he's been dipped in molten metal and left out to dry. Then, his eyes start to glow. The characteristic "pixelization" of the X parasites covers his entire body, and we meet Neo-Ridley, giving maybe the biggest roar of any enemy up to that point as he suddenly becomes twice the size that he was before. Oh, Crap! indeed.
- Something that doesn't get brought up enough with regards to Fusion is the overall sound design. The game's soundtrack and ambient sounds ratchet up the dread like no other Metroid game before it. The music has a much more dramatic and heart-pounding tone that constantly makes your heart tense up as you navigate the desolate station while creature sounds and definitely the sounds the bosses make can induce rampant panic attacks that numb your focus and make you react instinctively instead of tactically because you just want it to go away. Play this game with your headphones on and in the dark and it is grade-A Paranoia Fuel.
- The setting for this game is unlike any other Metroid game. Samus is no stranger to lone wolfing it but due to the circumstances, this game truly makes you feel dreadfully alone and exposed. Everyone on the research station is dead and it's overrun with barely-understood parasites, one of which is basically a walking armory. In other Metroid titles at least Samus feels like she's on somewhat equal footing with her foes but in this game you almost constantly feel woefully underequipped, having to resort to sneaking around and avoiding situations instead of confronting them head on. You're in their house. Plus every so often something will go haywire and send the unsettling slow pace into frantic overdrive and you won't know what's wrong or what to do for the first few minutes.
- SIXTY SECONDS TILL IMPACT.
- At one point, rapid plant overgrowth causes the station's power to go out completely, disabling everything, including the save points. A save point can be seen as something of a perch a player can go back onto if things get scary. Now you don't even have that to comfort you.
Nightmarefuel / Metroid Fusion