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Nightmare Fuel: Defiance
Datak's rage after killing the Spirit Riders is really disturbing. His spitting and inhuman hissing is very unsettling.
We get to see an Earth Republic prison camp in Season 2 - inmates are kept in a large pen, open to the elements, and "fed" by being tossed scraps of food that they're left to fight over.
Irisa's Imagine Spot toward end of "The Opposite of Hallelujah" is definitely this, as they ride together in the dark, father and daughter finally reunited, and then she casually reaches over and slits Nolan's throat. This, plus her murder of a random Castithan woman back in AngelArc, indicate that the Kaziri has done something very bad to her mind.
After being forced by Irzu to murder poor, innocent Bertie, Irisa tries to break free of Irzu's control by shooting herself in the head with a rifle. She manages to pull the trigger, but it doesn't kill her. It does, however, blow a nasty hole in her usually lovely face. Good Thing You Can Heal...
And then the situation gets even worse with the reveal that Irisa hasn't been killing people as she thought, but is instead carrying out some sort of Assimilation Plot involving metal tendrils moving from body to body via the mouth. Pleasant dreams after that.
Datak gets out on probation. Having learned that Stahma has been taking over his business in his absence, he promptly returns home and makes a brutal attempt to drown her in the family tub.
He actually gets creepier in the following episode, trying to reassert his authority by doubling down on Castithan traditions. Fortunately, this is quickly derailed when Stahma has him beaten to a pulp for scarring Alak and takes over the business.
"This Woman's Work" features the first appearance on the TV show of a Gulanee, and it (she?) is terrifying. Clad in an Uncanny Valley-inducing robotic containment suit, with a shriek like a banshee and a touch that fries flesh. Further, our heroes didn't even try to reason with her. Either the Gulanee are too alien to communicate with, or they just don't care.
"If You Could See Her Through My Eyes" features honest-to-god cornea harvesting. They even show it from Rynn's perspective. Try not to cringe. Try and fail.
There's something very...unsettling at watching Christie imitate Stahma's mannerisms, even taking her name. She does it a little too well.
On top of that, she's chumming around with a man that's twice her age, if not more. There is so much squick in this... Creepier still is the fact that he seems to realize as much, but then just goes with it.
In "Painted From Memory," while talking to Pottinger about lobotomizing the Kenya clone, Yewll gets very scary for a moment. We catch a brief glimpse of the Retired Monster behind her eyes, and we remember how dangerous she really can be. So much so that Pottinger actually takes a step back from her out of fear and revulsion.
Pottinger: Doesn't it bother you? Yewll:(Death Glare) I've done worse.
In "Doll Parts", not only does Christie turn out to be the one who killed Diedre and framed Alak for it, but when she admits it to him, she's completely calm, even copying Stahma's mannerisms while doing so. She then basically considers herself a Castithan woman, and gains Stahma's theme song. While also an awesome moment, it's all very disturbing.