Everything about Brainwave (except when he has amnesia or in certain flashback/video diary scenes set in his younger days), from his dispassionate monotone to his sadistic torture of Courtney to the way his own son is so obviously terrified of him from the first time they appear together.
Jordan's tender goodbye to his dying wife (complete with their son giving her a drawing) experiences some chilling Mood Whiplash when her last words are for him to continue his mission and kill anyone who gets in his way.
Dragon King's introduction, between the inhuman features visible through his mask and the way he eagerly asks for Wizard's body right after saying the two of them hated each other, either to experiment on or to eat.
Yolanda being tempted to use her new costume to stab Henry in the back with some very sharp claws.
The Reveal about poor Denise Zarick's fate. After prominently featuring in several other scenes (Brainwave visiting Wizard's house in the middle of the night to warn him of the new Stargirl, in the back seat of the car as she prepares to leave Blue Valley), we see the black cat wandering through the pick-and-pull lot looking for attention. Pat recognizes it, follows it through the lot...and discovers Denise's abandoned car. The audience is treated to close-ups and slow pans to show the damage, the broken cat carrier, and nothing left inside but Joey's magician's hat on the seat. Then the camera pans back to show the immense dent in the car's side before panning up to a lonely shot of Pat standing speechless before the screen goes to black with a lonely piano piece. Chilling.
In the middle of an intense bullying session, Cindy threatens to sic Dragon King on her stepmother unless Bobbie lets her drink alcohol, making Bobbie frantically beg her not to before procuring some wine.
Henry's intense stares and rants as he begins to adopt his father's misanthropy.
The flashbacks to how Yolanda's life was utterly and completely ruined in the course of a single morning, thanks to a guy she loved and trusted.
Larry slowly, cheerfully gives Pat a No-Holds-Barred Beatdown, utterly outclassing the hero and showing no qualms with brutally murdering a guy he used to get on with, then go after his son.
In the first season finale, when the machine is being used and the little girl in the street begs in confusion and fear to know what's wrong with her daddy, then clings to him as he fights the mind-control from within, to the appearance of blood at his ears. Jordan appearing and reassuring with sociopathic calm (and what he clearly believes is real sincerity and warmth) that her father is just being changed into a better man is the icing on the cake.
Season 2
Season 2 is essentially Nightmare Fuel: The Season due to Eclipso's psychological torture.
Eclipso using Cindy to kill her own stepmother is chilling.
The Shade invokes to Courtney that when he is afraid of what Eclipso can do, then Courtney should be scared out of her mind.
The respective death and "death?" of Issac Bowen and Cindy Burman.
The ambiguity of Cindy's demise is all the more frightening since we don't yet know if she is, in fact, dead or is suffering a Fate Worse than Death, or what state she'll be in if she does come back.
Come episode 10 and Courtney herself is subjected to the same fate.
Season 3
Pat and Sylvester describe the Ultra-Humanite, and how—just as in the comics source material—he surgically implanted his brain into the body of actress Dolores Winters and stole her life, even winning an Oscar while in her place. Everyone else present is naturally incredibly horrified and can't believe the kind of monster they find themselves up against.
Sylvester also describes it as being one of the toughest foes the JSA ever faced. Given that the new JSA doesn't have anywhere near the raw power or the experience the old team did, this is particularly frightening.
The Reveal in the penultimate episode that Sylvester has been Dead All Along, and the Ultra-Humanite has been in his body while the albino gorilla's body — formerly occupied by the Ultra-Humanite's brain — is now being occupied by the Not Quite Dead brain of Dragon King. Along with Icicle, these three villains have been playing the heroes right from the start and the JSA lost before they even knew what they were doing. And the icing on the cake is that the Ultra-Humanite then buries Pat alive, the one saving grace being his Bond Villain Stupidity rather than killing him directly.
Rick, after having removed the one-hour limiter from the hourglass, tries to take it off in 3x12. The experience is shown in a chilling P.O.V. Cam, with blurry visuals and Rick moaning in pain.
