Nightmare Fuel / Super Mario Bros. 3

• The mini-fortress theme. Whereas the original SMB's theme gets its spookiness from how frenetic it is and its use of Drone of Dread, this one relies more on minimalism, spreading out short bursts of notes with distinct periods of silence.
• The Angry Sun made some too scared to play past World 2. It just floats in the sky with an angry scowl on its face... only to suddenly swoop in and attack you halfway into the level. Even if you do get past World 2, it makes a surprise appearance again in stage 8-2, when it comes after you from behind a hill. Oddly enough, though, you can get rid of it with a mere Koopa shell of all things.
• Boss Bass, a hungry, fast-moving fish that constantly chases you as you race against time to get to high-ground as the water level rises... if you don't make it to high ground in time, or worse, fall in the water, he will swallow Mario in one gulp, no matter how big you are, and you instantly lose a life. Unlike the Angry Sun, you cannot get rid of him for good — even if you do kill him with the Fire Flower, he will return just a few seconds afterwards, just as ready, willing, and able to devour you as before.
• Chain Chomps are scary enough as-is. Then you learn that they can actually break loose from their chains if left alone long enough. Have fun.
• World 6, Ice Land, has an incredibly eerie theme which stands out from the rest of the game's soundtrack. In stark contrast to the jolly and peaceful music and atmosphere most ice levels in the series seem to be made with in mind, it has a terrifying feeling of isolation that sounds appropriate for being trapped and lost in a blizzard. The All-Stars version isn't any better, and it's appropriate it'd be remixed again for when Mario receives threatening emails from an unknown stalker in The Thousand-Year Door.
• In what is probably gaming history's first instance of liminal space horror, World 7's first mini-fortress is completely abandoned, save for the Boom-Boom at the end. There's one room where you can see enemy-related infrastructure, such as the center posts for the Rotodiscs and the lanerns for the Hot Feet, but the enemies themselves are missing. Hell, the white platforms for Streches are there, but there's no sign of Boos or any ghost related enemy at all in the level! Also the exit is non-obvious, and someone who doesn't think to use Raccoon or Tanuki form to fly up to the Warp Pipe may get stuck and die of time over all alone. It definitely gives off the feeling something horrible happened in the fortress, be it a natural disaster or something else entirely, that not only wiped out the original inhabitants, but also took the dead with them, and you're just traversing through the aftermath.
• After completing World 7, you'd maybe expect a letter from Peach thanking you for saving the seven kingdoms. But nope, the letter is from Bowser this time, who has revealed that he's kidnapped her! And instead of a dreamy jingle playing with the letter, you get the first few notes of the boss theme and a flashing red background for good measure.
  "Yo! I kidnapped the princess while you were running around. She's here in my castle, if you dare to try and rescue her. Ha ha ha..." -King of the Koopa
• World 8, Dark Land can be a severe mood whiplash from the relatively bright and cheerful worlds before. The color palette switches to crimson-ochre tones like you've gone to the hell where Bowser presides, and doesn't pull punches with giant skulls adorning two map regions. Not surprisingly, there are no mushroom houses or minigames to be found.
• In World 8's second submap, you can be randomly dragged down into a dungeon-like level by a disembodied hand. There's no telling when it will happen, and can catch first-time players off-guard. The GBA remake ups the horror by adding a cutscene to this submap, where Peach is dragged down a pipe, screaming Mario's name.
• Due to the color limitations of the NES, Bowsers Castle — rather than it appearing as the chateau-castle it's meant to be — looks more like an Eldritch Abomination that is made of pink flesh.◊ ready to swallow Mario up. The four giant mushrooms within the citadel walls might also add to the otherworldly feel. This was "corrected" in the updated remake◊, Super Mario All-Stars thanks to the enchanced color palette allowing it to appear as an actual castle, with a likeness of Bowser's skull built atop. The interior of the castle might not be much comfort either, as it appears to be built out of crimson fireplace bricks seen nowhere else in the game and...
  • The laser-shooting Bowser statues in his castle. They look nothing more than typical castle decorations, until you approach them and they suddenly start firing lasers at you. Worse yet, there are no visual differences between the laser-shooting statues and the harmless ones, so you can easily be caught off-guard.
• The opening to the GBA remake goes into detail how much of a threat the Koopalings really are. In the middle of a raging storm, Larry Koopa's Airship flies over the Grass Land castle, where he busts inside through the roof. Toad charges forward in an attempt to attack, but he instead bounces harmlessly off of Larry and is left dazed. Larry then attacks the king, steals his wand, and transforms him into a Cobrat as a helpless Toad can only watch as Larry leaves the way he entered.