- Star Trek II: The Wrath of Khan gets away with a lot because the PG-13 rating didn't exist back then, so the movie went as far into PG as it could without getting an R rating.
- The thought that whatever happened on Ceti Alpha V since Kirk marooned the Botany Bay survivors there was sufficient enough to drive Khan of all people to the point of utter madness is pretty nightmare-inducing. In "Space Seed", Khan was himself a case of Nightmare Fuel; in the movie, he's gone completely psychotic.
- We see one of the scientists from Regula One get vaporized by a phaser. It's not quite an Instant Death Bullet, as we can hear the man's quickly fading scream of agony as he is vaporized.
- Some of the injuries suffered during the battles between Enterprise and Reliant. Scotty's nephew, who we find horribly burned, and another crewman in the torpedo bay who gets engulfed in flames during the final fight.
- Khan's "pets", the Ceti eels. Two to three-inch long worm-like creatures with pincers that burrow into a person's ear and attack their brain, making them easily controlled and very susceptible to suggestion. A Puppeteer Parasite is deposited into a helmet, which is then placed onto a restrained crewman's spacesuit. The crewman, and not any Red Shirt, but Pavel Chekov, is helpless to do anything but scream helplessly as the thing crawls into his ear. Even worse is when the captain of the Reliant fights back against the creatures, and kills himself with a phaser set to disintegrate. Forget that's it's science fiction; this scene qualifies Star Trek II as one of the best horror movies of all time. The way Khan's looking at them dispassionately as this happens makes it worse.
- Similar creatures make an appearance in Star Trek (2009): Centaurian slugs, used by Nero on Captain Pike. What could be worse than a bug being forced into your ear? A bug being forced into your mouth.
- Captain Terrell, turning his own phaser on himself and firing. It's the way Paul Winfield plays it. He totally sells it. Truly horrifying.
- Though we don't see them for very long, the adult forms of the Ceti eels. Khan quite literally plucks two of the young ones off its body, the thing has quite a grip, and frequently makes a very unsettling sound. And Khan visibly exerts some amount of effort to keep the thing pinned while he plucks the young larva, giving a Five-Second Foreshadowing that these things are far more dangerous than they might seem.
- There's actually a number of things in this movie that are unsettling: the hanging corpses in the space station, Khan's finale where his face is half burned...
- Khan's Fate Worse than Death speech when Kirk tells him to come down and fight:Khan: I've done far worse than kill you... I've hurt you. And I wish to go on... hurting you. I shall leave you as you left me, as you left her... marooned for all eternity in the center of a dead planet... buried alive... buried alive...
- The crew of Regula One murdered and hung like sides of beef in a freezer. The novelization goes into detail about Khan's stop at Regula, which is even more nightmare-inducing.
- Pay attention to the sound effect that plays when someone is vaporized with a phaser. It's not just the energize sound of the phasers. There is also the echoing sound of a scream.
- Peter Preston's mangled body.
- What we are verbally teased to what happened to Khan and the crew of the Botany Bay during the fifteen-year gap between "Space Seed" and this movie. Ceti Alpha Six, a planet close to the Eden-like Ceti Alpha Five, exploded, shifting the course of Ceti Alpha Five just to the point where the environment becomes a hostile, barren wasteland and the only indigenous life form are the aforementioned Ceti Eels, which managed to KILL MORE THAN TWENTY MEMBERS OF HIS CREW, INCLUDING HIS WIFE WITHIN A FEW MINUTES, causing him to go down a brutal Sanity Slippage!
- The novelization of that time inbetween the episode and this movie shows us what happens with prolonged exposure. Marla is deliberately infested with the eels by a member of the marooned crew with Khan's who's making a power-play to take Khan off the throne. Marla has orders to get close to her husband and kill him, and gets as far as his side, before her own iron will finally kicks back in and she kills herself, rather than harm the man she loves, dying in Khan's arms. Khan doesn't take it well.
- For that matter, how the movie sets up Khan's big reveal to Chekov and Terrell on Ceti Alpha V. The two beam down to a barren, dusty wasteland and hurry into what they think is an abandoned storage locker. In snooping around, Chekov discovers the words "SS Botany Bay" etched into a belt, which he immediately connects to Khan and goes into a Stage 4 Freakout, telling Terrell to leave immediately. But when they open up the door to go outside, you see Khan and the rest of the Botany Bay survivors just standing together on a hillside waiting for them, all decked out in creepy nomadic clothing. Very well executed nightmare fuel indeed.
- Before VHS and DVD boxed sets, if you were a die-hard fan and remembered the episode Space Seed, you were going "Oh, Crap!" right alongside Chekov as soon as you saw the name Botany Bay. If you weren't, his sudden, frantic cries of "We have to get out of here now! Damn!" lets you know something seriously bad is about to happen. Either way, very scary.
- Chekov's creepy, dispassionate smile while telling Dr Marcus that they are ordered to take Genesis (which doesn't change as he is being yelled at by the outraged scientists). Also the fact that his face immediately falls to a blank stare as soon as he hangs up.
- Captain Terrell's Dissonant Serenity and Thousand-Yard Stare as he describes Khan's rampage on Regula 1 is extremely unsettling.
Nightmare Fuel / Star Trek II: The Wrath of Khan