History NightmareFuel / Ben10

* Khyber's TrophyRoom is filled with bodies and bodyparts from various aliens that have been confirmed to be sentient over the course of the show. This includes an Ultimate Humongousaur skull, ''[[TransformersAnimated Grimlock]]'''s sword, a Terraspin shell and many others...

** It's then revealed multiple girls suffered the same fate. As the protagonists try to figure out what happened with the help of who seems to be the local superhero. Eventually turns out said hero, despite possessing light powers, ''is'' the responsible: he charges his powers by feeding over energy from schoolgirls he seduces, eventually turning them into zombies slaves that he relies on to feed him even more. His habit to drain energy from them is played subtily like rape. To make matters worst, he succeeds in draining ''Gwen''.

** This was retconned as the Hightbreed merely imprisonning him ''Ultimate Alien'', but still creepy...

Let's face it, a [[WesternAnimation/{{Ben 10}} meta]][[WesternAnimation/Ben10AlienForce -series]] [[Ben10UltimateAlien about]] [[Ben10Omniverse Aliens]] ''has'' to involve some horror at some point.

* It's kind of a scary world to live in because of how easily it seems the world is doomed. One xenocyte? Your whole world contains nothing but [[FacelessMooks DNAliens]] in short order. Death Star class ray guns are available to even ''comedic'' villains. Many planet, including [[InsignificantLittleBluePlanet Earth]], are considered so insignificant that the [[SpacePolice Plumbers]] will sometimes not even bother ensuring security to protect them, meaning few people would lay a finger if someone suddenly decides to conquer or destroy Earth (even in the light-hearted show Ben10Omniverse, a character treatens to destroy Earth [[DisproportionateRetribution because a guy living on it won't marry his daughter]], and encounters ''no resistance whatsoever'').

* Depending on the alien Ben is turning into, some transformation sequences can involve a large amount of BodyHorror:

** That same episode gives us Toepick, one of Ben's aliens. At first it seems to be an ordinary alien with a helmet. [[PleaseKeepYourHatOn Then the faceplate opens, revealing it's horribly grotesque face]]. [[TakeOurWordForIt We're never shown its face]], but if Psyphon's screams of terror are any indication, it's better if we didn't.
*** ItGetsBetter: We've already established that Zombozo is NightmareFuel incarnate, and yet Toepick terrified him at least as much (maybe worse) than Ghostfreak.

** Not to mention the fact that Ben as Echo Echo only survived him [[GenreSavvy by having one of his selves hidden]]. [[spoiler:Ultimate Kevin]] ''genuinely'' thought he was killing Ben and didn't hesitate a second.

*** ItGetsBetter: We've already established that Zombozo is NightmareFuel incarnate, and yet Toepick terrified him worse than Ghostfreak.

* Inspector 13's really, really, really horrible EvilLaugh. Even Ben is creeped out.

* Aggregor; the guy is probably one of the most competent villains in the whole serie, maybe the whole franchise; He did nothing but win for all his story arc, usually using the protagonists as pawn. And he was ready to absorb (which might as well be kill) five aliens in order to get their powers. Even worst, his final plan was to [[spoiler:[[PoweredByAForsakenChild absorb a Celestiansapien child]]]]. This guy was in many way similar to Kevin 11 in the Ben 10,000 future where he didn't reform.

--->'''Simian''': T... this is a horrible mistake!
--->'''Highbreed''': It sure is. We distinctly told you to bring the crystal. Maybe you misheard us. Maybe ''you'' need to have ''your'' ears cleaned... (loud hissing noises come from the acid dripping out the ear cleaner [[GoryDiscretionShot offscreen]] as the episode ends)
** This was retconned as the Hightbreed merely imprisonning him Ultimate Alien, but still creepy...

* In the episode "Last Laugh", [[Ripjaws:FishPeople]] deals with a robber by ''pulling him underwater''. The robber isn't seen again

* The Psycholeopteren whose DNA Khyber was taking is kinda hardcore. It makes you see your fondest desire, but it is a predatory beast. Most LotusEaterMachine scenarios give you a long time to realize the world's wrong and marshal your HeroicWillpower, or your friends come and rescue you, or something. This thing, you've got about five seconds in la-la land before this thing ''eats you.'' And just think, ''aliens use this thing as a GRatedDrug.'' If it's improperly contained, enjoy your [[DarwinAwards Darwin Award]].

** Heatblast has Ben's skin being gradually covered with rock then being set of fire;

** The nastiest scene is its death. Ben has acquired his first new alien, Cannonbolt, but the tick can't be harmed on the outside. Instead, Ben, as Cannonbolt, goes ''inside'' the tick and demolishes its ''inner organs'' until they ''leak out alien blood'', smashes athrough all its ribs, and causes it to explode, spilling its goopy entrails everywhere. Fortunately, Yellowstone reverts back to normal, but there's still the matter of cleaning up the mess... poor Ben.

* [[MonsterClown Zombozo]]; not only is his look disturbing, with a zombie-like face and a long, inhuman tongue, but the guy feeds on people's happiness. Not scary so far ? Well just see what is left when he has sucked most of it...

** When he returns in ''Ultimate Alien'' he's using his power to its maximum level, outright turning to dust anything he hits with it. He also gets a reputation as HeroKiller - he's ''hunting'' Bens one parallel dimension at a time, and ours is just next on the list. ([[spoiler: It turns out they're not dead, though: his {{Mooks}} are the alternate Bens, brainwashed.]]) Ben gets lucky in that his alien forms leave his human form behind unharmed if they get dusted, though he loses the ability to transform into that alien. (They're restored, though.) He's no longer getting the horror movie treatment, but you still hold your breath with him.

--->'''Highbreed''': It sure is. I told you to bring me the crystal, and you didn't. Maybe you misheard. Maybe ''you'' need to have ''your'' ears cleaned... (loud hissing noises come from the acid dripping out the ear cleaner [[GoryDiscretionShot offscreen]] as the episode ends)

* It's kind of a scary world to live in because of how easily it seems the world is doomed. One xenocyte? Your whole world contains nothing but [[FacelessMooks DNAliens]] in short order. Death Star class ray guns are available to even ''comedic'' villains. Many planet, including [[InsignificantLittleBluePlanet Earth]], are considered so insignificant that the [[SpacePolice Plumbers]] will sometimes not even bother ensuring security to protect them, meaning few people would lay a finger if someone suddenly decides to conquer or destroy Earth (even in the light-hearted show Ben10Omniverse, a character treatens to destroy Earth [[DisproportionateRetribution because a guy living on it won't marry his daughter]], and encounter ''no resistance whatsoever'').

* Eon in his first appearance was damned ''creepy.'' What do you do when a TimeMaster doesn't like you? [[Series/DoctorWho Basically, run]]. His time ray causes RapidAging, and the first guy we saw him used it on looked like a half-decomposed corpse... and was still alive. His body had become so brittle that at one point, a not-very-hard touch causes the guy's arm to break off (and we learned his ability to feel pain was very much intact.) You probably sighed with relief when the poor guy [[AlmostDeadGuy finished his exposition]] and died. There's also the way he stalked Ben: staying out of step with reality, he could follow Ben anywhere unseen. You know that weird little blur in your class picture? That's him. Watching you. It's hard to describe, but the handling of him when he'd approach Ben was more like a horror movie's supernatural foe than one of Ben's standard enemies. Also, when he's around, ''no one'' can help Ben, because Eon is fond of TimeStandsStill. You and a bunch of heavily armed Plumbers are getting ready to show this guy who's boss... and suddenly Robert Picardo starts to talk... very... slowly. Then you're the only one moving... you, and the guy responsible for the most FamilyUnfriendlyDeath in franchise history, who hasn't done it to you ''yet'' because he ''needs'' you, and who's been looking over your shoulder at school and at home and ''everywhere.'' Unlike Vilgax or Diagon or any other BigBad, there's not an alien in Ben's arsenal[[hottip:*:Okay, he'll eventually get Clockwork.]] that makes Eon less of a threat. Every time Ben encountered him - and all the times Ben had no idea he was there - Eon could have killed Ben at his leisure and there'd have been nothing Ben could do. His plan needed Ben alive and that's why Ben is still here.

* [[BigBad Vilgax]] can be quite terrifying from some angle; his voice, provided by SteveBlum, is creepy by itself, especially when he is mostly seen in the shadows in the first episodes. When he finally ends his treatment and goes after Ben of his own, he proves to be [[TheJuggernaut unstoppable]], defeating most of Ben's alien forms with nothing else than pure strength. And add to that he was ready to cut off Ben's arm to get the Omnitrix.

* It's kind of a scary world to live in because of how easily it seems the world is doomed. One xenocyte? Your whole world contains nothing but [[FacelessMooks DNAliens]] in short order. Death Star class ray guns are available to even ''comedic'' villains. Many planet, including [[InsignificantLittleBluePlanet Earth]], are considered so insignificant that the [[SpacePolice Plumbers]] will sometimes not even bother ensuring security to protect them, meaning few people would lay a finger if someone suddenly decides to conquer or destroy Earth.