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Nightmare Fuel: Gargoyles
The Hotel Cabal episode, which ends with Mace Malone frantically trying to find an exit to the sealed maze of traps all of which are designed to drive the prisoner insane. Word of God is he eventually died of dehydration.
The 11th-century flashbacks, in which Demona becomes gaunt and aged, make her look more like a vampire than a gargoyle: and she's quite enthusiastic with that spiked mace of hers.
On an initial viewing, it seemed like a woman-statue she smashed who was holding shopping bags ("Let Me Get That For You") was in fact *pregnant*.
The Xanatos Goon Squad in "Monsters", being dragged down in their submarine to a watery grave by some very angry plesiosaurs.
Jackal in "The Green" when he fantasizes about smashing stone Gargoyles by day. Frightening enough as it is, but then he whips out a chisel and carves Goliath's face to look like his.
His entire killing spree in Grief. A sociopath now has complete control over life and death. Screw Do Not Fear The Reaper, I'll take The Grim Reaper any day over a crazed Jackal as my death god.
How bad is it? He starts small — a tree withers away, a couple of machines are turned to scrap metal, and a pair of Nile crocodiles are reduced to skeletons. The last thing we see him do? He lays waste to an entire thriving city!
The whole concept of Thailog, once you think about it. The guy has Goliath's strength, wordy knowledge, and combat skill coupled with the knowledge and manipulative genius of Xanatos and the scientific knowledge and goofiness of Sevarius, but without a trace of any kind of morality. Be afraid... be very afraid. Xanatos is afraid, you should be, too.
Sevarius himself is creepy enough as is; this tropette was thoroughly squicked by the episode in which he discovers Angela. It wouldn't be so bad, except for the scene in which he acquires the gargoyle... unconscious... comments on his delight at having found "an adolescent female!"... and starts playing with her hair, a rather rape-y expression on his face. I know his pleasure was in the potential of the discovery, and they probably never meant to imply anything sexual about it... but it still made my skin crawl.
The werefox. The gratitous use of Jump Scare gave this troper a few nightmares as a kid.
To say nothing of Fox's transformation, especially when she's reaching out to Xanatos and screaming, before the were takes her over.
The episode that first introduced Coyote was often skipped in syndication, probably because of the scene in which Bronx knocks Coyote to the deck and mauls his head. It just barely gets past the radar because anything you do to a robot is OK: but it's a very realistically depicted and lethal-looking savaging - and a first-time viewer would probably still assume that Xanatos is the guy in the armor.
The gang's fates in "Future Tense." Broadway was blinded in a fight and his eyes are now two black holes -that's before he is shot and killed. Bluestone, Bronx, Claw, Angela, Brooklyn and Demona are all vaporized on-screen. Xanatos also kills his own son with a smile on his face.
The Goliath Chronicles episode "Genesis Undone" stands out as rather horrifying. The deterioration of the Manhattan clan clones is unsettling to say the least. We then get to watch as they all ( including Thailog) writhe in agony before turning to stone, at night.