Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Super Smash Bros.
Toon Link doesn't look so adorable now...
There are twelvenote The Legend of Zelda, Metroid, Pokémon, Super Mario Bros., Donkey Kong Country, Kirby, MOTHER, Pikmin, Fire Emblem, Star Fox, Yoshi's Island, and Animal Crossing other TV Tropes pages detailing the Nightmare Fuel in different Nintendo games. There are also entries in the main Video Game section detailing the frights in other Nintendo games. So when you combine characters from all the recognizable Nintendo franchises in one fighting game series, it might be handy to take a few deep breaths before playing.
In order for Nightmare Fuel tabs to survive, a new writing style is going to be used, nicknamed Example Lobotomy. Basic rules: just list facts as they are, don't just say "character X" or "the X scene" (such zero context examples will be zapped), spoiler policy to be determined on a case-by-case basis, italics to be applied to works' names only and not to give emphasis on what tropers say. "X scared me" is already implied by the mere addition of that example by the troper.
In the first Super Smash Bros., players fight constantly against their fellow creations, killing them all, ultimately annihilating the creator, who had been sadistically forcing you to fight for his own dark amusement. All this knowing that he was the only thing giving you life, turning the whole thing into an extended quest to die, and essentially lecturing the players about how awesome the "Cool vs. AwesomeMascot Fighting" really is. That, or the game's plot is about a kid playing with his toys, and the last boss is the kid using his hand to represent a "big villain".
Metal Mario never says a word, he doesn't even flinch when hit, and worst of all, he never runs: he does Unflinching Walk towards the player, not seen as a menace.
In the Kirby games, the eponymous protagonist inhales the opponent and swallows it. In the Smash Bros games, he doesn't. The fact he restricts himself in order to "play by the rules", in turn, makes his abilities in his native series worse in comparison.
It's worse than that — the fact that he achieves exactly the same result whether he swallows (and by extension kills) the things he swallows or just spits them back out shows that he enjoys killing!
Brawl's Link has an alternate costume that turns him into Dark Link, with black clothes, gray skin, and red eyes: pretty standard fare. Doing the same with Toon Link's big, cat-like eyes results in the freaky page image seen above.
Similarly, Pit has a "fallen angel" costume, who ultimately resulted in an actual Dark Pit in Kid Icarus: Uprising. Though, Dark Pit is nowhere near Nightmare Fuel material in Uprising, being a more cocky and brash version of Pit.
In the Subspace Emissary game, Brawl's "Adventure" mode, there is a room in the Halberd Interior level in which the player character passes through a room with nothing in it bar unreachable glass cages that appear above and below him. Within these cages are various enemies that you encounter throughout the game, except for Mizzo. On the bottom row of cages, second to the right, there is this enemy that appears nowhere else in the game. It's just stuck in there.
The Armights fly out of the background with a creepy Evil Laugh when they appear. An Armight appears to be some sort of mutated, blue-skinned, dismembered head with two pointy tentacles and a Roman helmet. Funny mustaches aside.
Floows: floating, shadowy, wraith-like creatures with beady, red eyes that follows the player everywhere and regenerates as fast as they can be damaged; their main attack is to stand in place and let out a ghastly, tortured shriek as hundreds of smaller ghosts fly out of its body. The bio on its Trophy say it harbours "pent-up resentment" and "one part sadness, one part madness".
Puppits: corpse-like things with really long claws that just hang lifelessly from a string until they come across the poor unsuspecting character in their way, then they start attacking like crazy. Their trophy description points out that "nobody knows what's on the other end of the string".
Captain Falcon's Final Smash knocks a couple of characters near him onto an F-Zero track, where they look up to see Captain Falcon racing towards them in his Blue Falcon, which crashes into them and sends them flying. Anyone sensitive to real-life car accidents are better off not thinking about that one too much.
Given that most F-Zero machines tend to go over 900 km/h on a regular basis, imagine getting hit by something at those speeds...
Using it against the more cute or young fighters (Kirby, Yoshi, Ness, Lucas, etc.) makes it very painful and frightening to watch.
Mr. Game & Watch's Final Smash involves him turning into a giant octopus that hovers around with its undulating tentacles, with a constant ominous and unnatural humming sound throughout the whole thing.
When Pit summons Palutena's Army, the Centurions actually die after striking the enemy, as pointed out by the trophy: "their deaths are not in vain".
Even without prior knowledge of the Mother series, the boss battle against Porky is scary, either for the spider robot or for the boy in question - Porky - trapped inside it, apparently screaming; in fact, the entire Ruined Zoo level seemed to be slight-to-extreme Nightmare Fuel, because of how it contrasts with the brightness of the SSB world, and starts with Lucas from Mother 3 chased by an unstoppable Pig King statue. Prior knowledge of both Porky from EarthBound and the actual Ruined Zoo from the first Mother, if added to the picture, makes it worse.
Wario's part in that level is what makes him, for the first time, a believably frightening villain.
The fight between King Dedede and Bowser in the Subspace Emissary has Master Hand lying in the background, apparently bleeding to death.
Playing in stamina mode: instead of knocking fighters off the stage, you just beat them down until their HP drops to 0. The final hit is rendered in slow motion with the loser letting out a Death Cry Echo, and then their lifeless bodies just lie there on the field.
Fighting Master Hand is not entirely unlike one's action figures trying to kill one's hand; Crazy Hand, on the other hand, is creepier, since it idles spastically, has a few oddly creepy attacks, and is a tough boss, since it almost always brings Master Hand along.
Speaking of which, probably one of the worst original BGMs to ever come from the franchise is the Lonely Piano Piece playing right after defeating the Hand in the original N64 title. The so-called "Game Clear" music is indeed a lonely piano piece, but a horribly demented and off-key one, at that. Essentially, Pyrrhic Victory in musical form.
On the note of scary music? The Subspace theme in Brawl. It starts off as a very quiet, absolutely chilling tragic rendition of the normally uplifting theme on violin and flute. Combined with the vast, dark expanse of the alien dimension, it's guaranteed to send a chill down your spine.
Also, the "Save Room" music when you get to The Great Maze. There's a barely-audible rendition of the main theme playing slowly in the background. And if you needed any further indication of how twisted things are, look at the sky. It is torn. The best eldritch locations are ones that use familiar places, after all.
Tabuu: floating digital ghost, borderline SNK Boss with highly damaging attacks, including his signature, which can kill you in one hit on standard difficulty. This guy controlled Master Hand though chains of light planted beneath his skin, hence the "bleeding to death" bit mentioned above.
Also note: he wasn't created by Master Hand. The creator of the whole game world was controlled and then Curb Stomp'd by an "alien" entity. Does this mean there are even worse entities now? And how does Subspace actually fit into the bigger picture? Chew on that for a while.
The scene near the end where the heroes have finally fought their way to the heart of Subspace, with Mario leading them, ready for the final battle: and then Tabuu "kills" them all at once before they can do anything. Their Mass "Oh, Crap!" is rendered in slow motion for added drama.
It gets worse. After this scene, you're sent to the world map, with one more location... and just to drive the point home, look at your available characters menu. EVERYONE IS GONE. Combined with how everything is silent, dear Jebus...
Giga Bowser's introduction in Melee. Just after getting to the end of Adventure Mode and beating Bowser, Bowser's trophy suddenly lurches back on stage with a loud thud, and then mutates into a colossal, far more vicious-looking, SNK Boss version of Bowser. And his transformation ends with a silent roar, complete with Glowing Eyes of Doom that freezes in frame while the actual fight starts loading.
Said "more unsettling version of the Final Destination theme" also makes an appearance for Bowser and King Dedede's battle in the Subspace Emissary. Which really makes sense, considering the main theme of Melee is remixed from the Bowser stage music in Super Mario 64.
Giga Bowser's redesign in Brawl, which makes him bigger and much more terrifying.
In the Smash Bros. Brawl world, apparently, all the main characters are trophies that exist to fight and nothing else. Thus implying parallels between Super Smash Bros and the Norse legend of Valhalla, an afterlife where heroes get to beat each other up for fun for all eternity, without having to worry about things like death and grevious injury.
At the beginning, the arena gets nuked with a Subspace Bomb, which basically pulls that part of the world into another dimension for Tabuu to do whatever he wants with. The characters flee before it is bombed, and the arena reappears later in the Subspace Maze for a boss fight, but nobody seems to care about rescuing the audience: nevermind the Inferred Holocaust to the R.O.B.s who got sucked into Subspace.
Zelda: Wait... what about the audience? Kirby Notorious K.R.B.: Who gives a shit?
Giant, purple, yellow-eyed Diddy Kong, another borderline SNK Boss not unlike Tabuu himself on the higher levels.
That part maybe, but in the fight itself, he's a bit of Nightmare Retardant: while Diddy's still giant, purple, and yellow-eyed, he still does the same things regular Diddy does. Including the taunts.
Shaydas has two heads, each with glowing red eyes, a glowing pink thing in its chest, blades for hands, and it's made of Shadow Bugs, which make up Mr. Game and Watch.
The scene titled "Ganondorf Takes Command". All the R.O.B.'s turn on the Ancient Minister, then set him on fire while sad music plays. Of course, the ensuing awesomeness as the Ancient Minister reveals himself to be the playable ROB and retaliates sort of mitigates this.
Donkey Kong's first appearance shows him smashing a Koopa Troopa into the ground, sending green shell-shards flying everywhere. While Koopa Shells are treated as clothing for Koopas in the Marioverse, here it seems more like Donkey Kong crushed his spine.
Pikachu stuffed into a jar and electrocuted, used as a source of electricity.
Bombeds decapitate themselves to attack, and then run around like a beheaded chicken until they grow a new head and repeat everything all over again. Their heads are bombs.
Some theories as to just how Tabuu managed to extract the Shadow Bugs from Mr. Game and Watch also fit this trope. One theory is that the Shadow Bugs weren't just "there", but were formed by liquid Subspace being injected into G&W's veins (or whatever organs serve that purpose), and the method of extraction was forcing him to cut himself open.
Samus getting worfed by Ridley: grabbed and scraped against the wall. It is fairly striking in its sheer brutality. So much so it got worked back into the Metroid series in Other M. Wall scraping and all.
Apparently, according to the SSBB Website, R.O.B's homeland was unable to be restored like the rest of the world, and R.O.B. is now the Last of His Kind.
The save points in the Great Maze. The background is desolate, and the sky is ripping apart to reveal the eerie darkness that is Subspace. The music sounds like you're in a Super Smash Bros. version of Hell, with a slow, unsettling rearrangement of the opening theme on top of it. The Great Maze and Subspace in general are pretty much Nightmare Fuel.
The Electroplankton stage, especially when it's paused, what with 2D characters, Super Drowning Skills-ish water, and the lack of music aside from that made by Hanenbows.
The Brinstar Depths stage is a giant piece of space debris that could be spun around by Kraid.
Not only is the stage creepy in that Kraid just comes out of nowhere from the lava and roars at the player, but the music is actually rather chilling.
Norfair in SSBB has lava plumes and occasional lava run-off appearing on left or right taking that portion of the screen.
The conversation with the Colonel if Snake uses the radio successfully while facing Luigi. They begin with discussing Luigi's second banana status but eventually move on to Luigi's magic powers. Suddenly the Colonel trails off and starts chanting "Lalulelilo... lalulelilo...": so either the Colonel is actually the fake Colonel from Metal Gear Solid 2, or Luigi just took over his mind. Creepy either way.
The Ice Climber's freeze glitch in SSBM tend to leave the frozen character in very awkward positions.
Lip's Stick: it causes a plant to grow out of someone's skull as it causes them agony. Look up Cordyceps and their effect on insects - the concept is the same. Its toy-like aesthetic and the utterly non-menacing appearance of its owner help to defuse things a bit though.
When Link and Zelda revive Ganondorf in SSE, he seems to be recovering from the beatdown Bowser laid on him (he's groaning and holding his head like it got hurt really badly). This implies that the trophy characters feel any pain they receive in trophy form.
Mr. Game and Watch has no concept of right or wrong and is able to be controlled by just about anyone, and is totally willing to go along with it no matter how mistreated his kind is, similarly to Wreck-Gar's Transformers Animated incarnation.
Aside from the Dedede Brooches, trophies cannot self-revive. And I Must Scream ensues if somebody ever falls in battle to someone who won't revive them, or worse, decides to either hide their trophy or keep it as an actual trophy because they hate them that much (or are that much of a Jerk Ass). And some of the earlier villains are implied to be in the second category, such as Wario.
It's not technically And I Must Scream because they're not conscious, but they could be sealed in a trophy-can for a very long time...
Normally, Brawl is able to take awesome music and make it even more awesome... with the exception of the Luigi's Mansion theme, in which case, it takes creepy music and makes it even creepier.
Interestingly it was the reverse with Ashley's theme, which in WarioWare Touched was a spooky uncomfortable song, where Brawl made it more upbeat and removed Ashley's creepy monotone voice.
In the Smash Bros Direct video, there are points where they show you a close up of a trophy and you're invited to guess who the trophy depicts. Well, one of the trophies LOOKED like Palutena from the back...but then it was revealed to be the nightmarish Pseudo-Palutena from Kid Icarus: Uprising, probably making everyone reach for their brown pants. The upbeat Kid Icarus victory theme playing didn't help matters.
Remember how the Ultimate Chimera in Super Smash Bros. Brawl did so much damage it was a guaranteed One-Hit Kill? In the fourth game, the Orne does more damage. And while the Ultimate Chimera is simply a goofy-looking magenta lion-like creature, the Orne looks like this.
The "Warning! Challenger Approaching" alarm in 64 suggested a mood of "get ready to fight!" However, the alarms in Melee and Brawl sound more like some abomination is heading your way and you need to get out of there fast.
You follow a blackened path upon Classic Mode, a road that leads to Master Hand and Crazy Hand. Though notably more intense, the battle proceeds as normal, and you do enough damage to Master Hand...then, something goes horribly wrong. Crazy Hand vanishes into a purple flame before reappearing inside Master Hand, the two writhing and convulsing before they explode open, a black mist filling the stage. The black mist comes together, and at long last, we see the joined "Master" will of Master and Crazy Hand alike: Master Core. This shapeshifting abomination is the very definition of a Smash Bros SNK Boss, and you will be horrified from beginning up until the very end.
Oh, by the way? For every significant blow you land, it sprays a bloodlike fluid for a few moments.
Another point to add is what form it takes every time for instance, At the Highest Intensity it first takes a form of some sort of Humanoid Shadow Golem that randomly spurts out two extra arms, then some sort of Quadruped beast with a Scorpion-like tail, next form is 5 Swords that can do tons of damage and combos, second-to-last form is a Super Mushroom sized version of your charcter in the same shadow-like mist, last form is a Nightmare Retardant in that all along it was a bigger version of a Smash Ball.