As The Legend of Zelda: The Wind Waker taught us, a cutesy art style doesn't mean the game itself has to be cutesy as well. This is better covered under tropes such as Surprise Creepy, Vile Villain, Saccharine Show and, most obviously, Art-Style Dissonance.
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.
- The endgame features, among other things, the scene where Linebeck saves Link, only for Bellum to possess Linebeck and turn him into a giant Phantom. Due to Art-Style Dissonance, there's next to nothing cute about this way-too-straight portrayal of Demonic Possession.
- On the Isle of Frost, players basically have to slaughter several Yook (as well as ones inside the Temple of Ice); this, despite having met one earlier, who promptly showed Link that they were clever, sentient beings, not mindless monsters. Made Nightmare Retardant when then they show up again later, with no explanation other than they ate too many bombs.
- The sandworms on the Isle of Gust get rather nasty when players move too quickly, which is about anything faster than the slightest tiptoe.
- There are also Tetra's telepathic cries for help, popping up at random intervals when loading a saved file. Complete with a nightmarish version of Zelda's Lullaby.
- Bellum himself. A giant yellow jellyfish-looking thing with eyes on his tentacles and either an eye in his mouth or teeth on his eyelids. And then there's his tendency to pop up out of nowhere.
- What about the first time a Phantom spots you?
- Speaking of Phantoms, the moment a Gold Phantom spots you, the other Gold Phantoms on the map can teleport right next to you.
- This game marks the only 3D appearance of the Pol's Voice so far, which were already a creepy enemy for their sheer otherness (i.e. recognizably lagomorphic features on an otherwise limbless, blob-like body). Here, though, we find out that they do, in fact, have a mouth, and it's their entire underside!