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Nightmare Fuel: Walrusguy
"Zelda Fails at Giving Tutorials". It lasts less than 10 seconds, but boy does it use that time well.
For those who don't want to Google it, the video is the first half of Zelda's tutorial in one of the infamous The Legend Of Zelda CDI Games. But then midway through she suddenly stops, bulges in a VERY ugly looking way to a very disturbing moan, then explodes.
We should note how the gem on her headband becomes an upside-down cross when her face morphs.
Then there's "Gwonam Gives Up", that may well be more lighthearted in tone, but its unnerving BGM as well as the apparently lobotomised Link has an overall Nothing Is Scarier feeling.