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Nightmare Fuel: Gamera
Gamera 3: Revenge Of Irys is chock full of these. In particular, the scene where Gamera is fighting against several Gyaos and pretty much just destroys the area with no regard for human life (except for one child he deliberately saves from a Gyaos). The people who survive the ordeal aren't grateful that Gamera stopped the Gyaos, they're terrified that they were nearly killed.
When Gamera blasts a Gyaos out of the sky and it explodes sending molten chunks of burning Gyaos-flesh raining down on unsuspecting civilians.
Irys. Imaging a creature that starts off as an Ugly Cute tentacled...thing with a shell, but quickly grows into an Eldritch Abomination. To make things worse, it feeds by impaling you with its tentacles and draining you of your body fluids. And, it tries twice to absorb a little girl so it can consume her and become strong enough to kill Gamera.