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Nightmare Fuel: The Iron Giant
If the deleted dream sequence is of any indication the Giant is one of many machines sent out across the universe to singlehandedly obliterate entire planets or, worse yet, may have already done such atrocities in the past.
Extra Fridge Horror in that the other robots might still be out there. And they might find Earth. And not be as friendly as the title character.
Given that the reason the Giant is good is due to Amnesiac Dissonance after hitting his head, as well as his friendship with Hogarth... how do we know that he wasn't returned to factory settings and his memory wiped, after he was hit by the nuke? Oh Crap.
The Iron Giant's transformation.
The enraged scream he makes during that is just as disturbing. Once you've enraged him, may God have mercy on your soul.
Mansley chloroforming Hogarth. It comes out of nowhere, and it's downright cruel.
Even worse is his Moral Event Horizon shortly before that. Up until this point, Mansley has been somewhat of a bumbler, and a lot of fun to watch as he repeatedly fails to catch the Giant. And then he very calmly threatens to make Hogarth's life such a living hell that he'd eventually be taken away from his mother if he doesn't reveal where the Giant is hiding. The worst part is the quiet, gleefully sadistic tone he's speaking in the whole time- he is perfectly capable (and willing) to follow through on any threat he makes, and he loves it.
The Iron Giant's first appearance at the power plant.
The bit from the old horror movie Hogarth watches where the mutant brain is presumably eating the man's head.