* If you watch the whole series without at least one squeak of terror, then you have more gumption than Jack himself. Some episodes were entirely built around NightmareFuel, like the episodes featuring the trip through a zombie graveyard, the Minions of Set from ''Jack In Egypt'', and the haunted house. Even the episodes not revolving solely around NightmareFuel have scenes that are simply traumatic, the frequent robot carnage that the censors let pass in every episode occasionally goes ''way'' beyond the borders of "not too bad;" once you reach dismembered robots impaled on spikes, things have gotten bad.
** Speaking of the graveyard episode there is a little bit of FridgeHorror that makes Jack's 'battle', and by battle I mean simply trying to survive, against Aku even more frightening. The form that Aku takes to finally overwhelm Jack is a huge black mass similar to the abomination he was a part of. Just a horrifying reminder that even though he's gained sentience and likes to toy with people using different forms, he can become a simple unnatural force if needs be.
*** His close up as he's about to stab Jack, his eyes look creepier than normal.
** Hey, I've got an idea, let's talk more about the haunted house! Jack follows a little girl to an old, decrepit house. He receives several nightmarish visions about what happened to the various family members that used to live there, all of them appearing to have been killed by some faceless horror. Not even Aku, just some creature with a sadistic streak. And that's only the first half.
** And the Minions of Set episode, its only against three beings. But these are creatures that Jack himself ''cannot'' stop. Any cut he makes the limbs grow back instantly and the minions continue the chase. Jack is forced to run and go on the defensive for rest of the episode as he tries to locate artifact pieces that will help defeat the minions. Nearly getting killed in the process. To say it's tense is an understatement.
-->'''Jack:''' These creatures are more powerful than anything I have ever encountered...
* Episode 15, "Jack's Tales", has Jack encounter a family of metal-eating robots. The robots, in a fit of hunger, rip each other to shreds, and the insides of the robots look just graphically enough like human flesh to creep you out.
* Aku himself suits this. Especially in his first appearance in the pilot.
** The two-parter explaining his origin adds to his terror. Apparently, he started out as this freaky monster inside the earth that would send large, deep cracks through the ground. The cracks were filled with him as he took the form of a tar-like substance, and he would then ''absorb living creatures'' to get stronger. At one point, a man calls out for his dog, goes to the back of his house, and sees one of the cracks filled with Aku-goop, and ''half the dog's leash sticking out.'' Doubles as a TearJerker when we hear the man's anguished and horrified screams.
** When Jack's father goes to stop Aku, charging into the forest of black, spiky trees with an army of samurai in tow. As they get closer and closer more trees burst up from the ground, and we [[GoryDiscretionShot hear samurai start screaming as their horses (now riderless) run by Jack's father]]. And then, after Jack's dad wakes Aku, Aku ties him up, slips into the ground, then pops back up by his kingdom and attacks it. Coupled with the guy's horrified face and the BigNo that follows, imagine how the people in the city felt.
** Even one of the most hilarious episodes where he's involved merely paints him horrific in a different light. He rounds up kids from within a capital city, with no reason given to them or their parents. The room they're led to is large, red and spiky as always, but has monitors of adorable, yet...off animals, which eventually switch off. The camera focuses on a large red throne in the room. And Aku just appears. No fanfare, no flashy effects, no booming monologue. [[NothingIsScarier He's just there.]] This is how he ''reads propaganda stories to children.''
* Demongo. The guy who stole essence. As in SOULS.
* The episode "Jack and the Ultra-robots" is worth mentioning, especially the [[DesolationShot second city]]. [[SceneryGorn Mutilated robots with horrific faces strewn about, some of them on pikes,]] [[SymbolicBlood and oil EVERYWHERE]].
* "The Aku Infection". Aku spreads some evil that infects Jack and soon starts to look scarier and scarier as it goes on.
-->'''Jack:''' I'm getting...
-->''(lifts up cloak to reveal Jack is looking and sounding more like Aku)''
** Right before that, possessed-Jack carves a robot bystander's face open [[DisproportionateRetribution for bumping into him on the street]]. We get a very close, slow shot of this happening; never before has the SymbolicBlood looked so terrifying.
* In the second episode there are silhouettes of crucified, intellectual ''dogs'', and it's implied that they are dead; Jack's reaction upon seeing it is entirely justified. Aku has been doing this since Jack's original time period to multiple races throughout multiple galaxies. For ''thousands of years''. That's horrifying. It makes you wonder if the universe was better off with the original abomination...
* "Jack And The Zombies". Some of those zombies were just plain freaky, like the long-armed zombie and the one that possesses Jack's sword. And when he falls into the crypt... that wail.
** The [[OhCrap look on Jack's face]] when Aku starts to use ''his own sword'' against him. Sure, Jack is still able to fight back, but a good chunk of that fight is Jack trying to run away or dodge Aku's attacks. Unfortunately, [[YouWillNotEvadeMe Aku doesn't let Jack escape that easily]]...
--> '''Aku''': Oh, Samurai? Where are you, Samurai? You can run, but you cannot hide, 'cause '''I can smell your blood'''!
* "Jack And The Lava Monster". As Jack comes closer and closer to reaching the end of an increasingly lethal series of traps placed by a cursed warrior, you see ''dozens'' of skeletons strewn about his labyrinth of death, killed in brutally horrific fashion when they each made a lethal mistake on the way in.
** Worse still, after [[spoiler: Jack breaks the curse on the warrior, he returns to human form- but the entire time he was locked away in that demonic prison, he was separated and left untouched from the natural flow of time. With the curse no longer keeping him filled with vitality, the effects of millenia wearing down on his physical body are finally unmasked- he reverts into a frail old man in an instant and dies. Fortunately, [[TearJerker he's carried off to the afterlife paradise of Valhalla to live in eternal bliss.]]]]
** Even earlier, Jack is traveling through the scorched countryside that was once [[spoiler: the Lava Monsters home, implied to be in Norway.]] It's bleak, cold, and littered with ash and dead corpses. On top of that, there's an ominous voice constantly beckoning Jack to follow it.
---> "Come... ''Come...!''"
* If the references are to be believed, [[http://i3.kym-cdn.com/photos/images/original/000/308/634/e06.png Samurai Jack is not only avenging his kingdom, but almost all Cartoon Network related shows from our childhood]]. That's right, Aku was responsible for the deaths and destruction of most, if not all, of your childhood favourites.
* Demongo, ''dear God.'' Not only is he an EldritchAbomination, he steals the souls and keeps the skulls of all the warriors he's slain. Skulls that he ''wears on his chest.'' Skulls that he can toss out to summon the ghosts of the fallen warriors to do his bidding, all of which have creepy blue mind-control eyes.
* In an episode called "Samurai vs Ninja" it gets downright hectic and overall a bit eery since you have two of the most deadliest warriors hunting one another in the art of Shinobi. All the while that they're both cladded for the appropriate elements. One fights in the dark while the other fights in pure blinding light. The whole fight in the very wooden tower is both a respectful mix of NightmareFuel and ParanoiaFuel. And to add even more fuel to an already deadly, adrenaline rushing encounter? The soundtrack throughout the whole fight! ... Horror cords and all. [[ShmuckBait Here]] [[http://www.youtube.com/watch?v=bmkxsQnNujI is the fight in its entirety]] .