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Nightmare Fuel: The Clue Finders
The aliens in 5th Grade.
The Reveal that they eat brains, and that they've captured everyone you've met on the island (and countless other people who sailed near it) to that end. Including Leslie's grandfather, which you see in a Jump Scare while a Scare Chord no less.
The Medusa rock with snakes coming out of her eyes in 3rd Grade.
Any given part of Goo Lagoon in 3rd Grade can be this to the squeamish, and kids tend to freak out at the extremely Beatles-inspired song.