- Inside the Magma Castle lurks an enemy not found anywhere else in the game—the Attacky Sack, a colorful, invincible patchwork ball with razor sharp teeth. Watch this,(at 2:40) and be enlightened.
- When a Yoshi is near death, the music is distorted and slow in a disturbing way.
- The health meter, which is normally a happy flower/sun, becomes blue, devoid of petals, and trembles miserably.
- Levels 2-1 and 2-2 are a considerably huge Mood Whiplash from before, what with the Bone Dragons, the Blarggs popping up out of nowhere, and the moaning fireballs.
- Two words: "Blargg's Boiler." Everything in that lava-filled hellhole is frightening, whether it was the giant monsters with GAPING MOUTHS that jump out of the lava and ROAR AT YOU or the lava ghosts... the noise they make... that SHRIEK...
- The last page of the game has four different themed castles, each of which is terrifying in its own way. Mecha Castle has machines that can crush or flatten you. Lift Castle is filled with buzzsaws that try and kill you. Ghost Castle, probably the least creepy, is full of Boos and other ghosts. Magma Castle is filled with lava and some of the creepier enemies.
- Mecha Castle, however, wins in Nightmare Fuel, as it features blades that pop out from walls and chase you, spikes, some saws, and the aforementioned one hit kill machines that move particularly realistically and violently. Magma Castle would be second, but it has a more epic and dungeon feel to it.
- Totaka's Song, composer Kazumi Totaka's Creator Thumbprint, is a bit more... unnerving... than usual in Yoshi's Story. It's the same 8-bit tune heard in The Legend of Zelda: Link's Awakening, Mario Paint, and others, but in Yoshi's Story, it is heard after staying on the Trial Mode screen for 2:07. Imagine listening to this song, so happy and cheery that it practically Tastes Like Diabetes, in an endless loop for more than two minutes... and then it suddenly drops to complete, dead silence before a somewhat-creepy 8-bit tune plays unexpectedly, then dead silence once again... and then it resumes the happy, cheery music like nothing happened.
- The Yoshis' hitpoints aren't tied to their health or vitality, but their happiness. This indicates that whenever Yoshi is out of hitpoints, he's actually become so cripplingly depressed that he can't continue the journey, fight or even move. The death sequence has Yoshi hauled off by Kamek's Toadies in tears to Baby Bowser's castle, too apathetic to try to stop them. Very dark for a game like this.
- How about the Bone Dragons themselves? And the music the plays on P.2 - Cavern itself...
- Level 4-2, "Jungle Puddle," is all good and fine for the first part. Then you get to the second part, with giant, invincible Blurps that eat you up, instantly causing you to lose that Yoshi. Those things caused nightmares in many a gamer back in the day, especially the younger ones. Even worse, players aiming for a Melon run must go in the water with those things to reach a pipe leading to a stack challenge.
- And it comes in two flavors! The red one who jumps out of the water and the blue one who spits water to try and throw you in. Trying to get all the fruits possible in the previous section is a normal practice here.
- Level 4-3, Piranha Grove. An entire forest of Piranha Plants, with you in the middle.
- The insta-death machinery in Mecha Castle.
- The castle itself no matter what course you're on.
- There's a code (press Z, L, A, and B simultaneously) to instantly kill your Yoshi regardless of health. It's likely kids would discover it by complete accident.
Nightmare Fuel / Yoshi's Story
Just because a game looks childish doesn't mean it can be immune from frightening moments...