[[caption-width-right:256:[[VillainousBreakdown NOT]] [[LogicBomb LOGICAL!]] '''[[VoiceOfTheLegion NOT LOGICAL!]]''']]

The premise may sound like your standard SaturdayMorningCartoon... but a closer look will reveal plenty of horrors.

[[folder:Code Lyoko]]

* '''EVERYTHING ABOUT XANA'''. The reason being that XANA was, and in fact, still is, unique among villains is that he never personally appeared or communicated with anyone throughout the entire series, with the exception of four/five episodes at most, out of ''97 total'', meaning the viewers were just in the dark about it as the characters, in fact, to this day, audiences re-watching the series have a hard time pinning down XANA's motives. XANA is literally the result of a villain who is NothingIsScarier as a character. If this isn't enough convince you how terrifying he is, just read the rest of this page to see how much it is related to XANA.
* "Guided Missile..." just that.
** This episode provides one of the most horrifying XANA attacks of the entire series. [[spoiler: Jeremie, who has a fear of flying, is trapped in a falling fighter plane about to hit the factory. Anyone who does not get heavy {{Fridge Horror}} was probably born after 2001. The military proceeds to threaten the tango contingency, which means shooting down the plane. The eject fails, which is Nightmare Fuel in of itself, as XANA has accessed non-electronic technology. But what truly sells it is just how horrified topical the situation is. They are caught in an impossible situation: kill Jeremie and the pilot, or let the plane fall. This becomes horrifyingly familiar, considering suicide bombings in today's world. If it hadn't been for Aelita, this episode would have had a {{Downer Ending}} in a truly horrifying way.]]
* The monsters XANA uses in Lyoko. Most of them are partially organic, partially mechanical. Kankrelats are small, cockroach-esque monsters with four mechanical legs on a round base and a single red robotic eye. Sounds unsettling out of context, but they're laughably stupid and often the comic relief of XANA's monsters. Others however are not. Here's a specific listing of them:
** Bloks, unlike the Kankrelats, are as large as a person in height, and have four of the creepy Eyes of XANA on each side of their rocklike shell. Their weapons range from FrickinLaserBeams to rings of flame to a freeze ray; in Season 1 more than a few Lyoko Warriors have been frozen solid by the Freeze Ray, unable to react to their friends being attacked and devirtualized.
** By far the most scary of the standard monsters (we're not even getting into the Scyphozoa or the Kolossus, but be patient, we will.) is the Megatank. Unlike most monsters which have a real life animal that they're based off of, the Megatanks are just ''alien''. They're huge black bowling balls that split in half, revealing an Eye of XANA, metal framework, and squicky pink flesh connecting its halves. Most monsters use the aforementioned FrickinLaserBeams, but the Megatank just shoots a ''plane'' of energy in a circular path; causing INSTANT devirtualization on a hit, and impossible to dodge if you're in its way, even if you're above the Megatank. That's not counting it simply flattening you as it rolls.
** Then, there's the Tarantula. XANA's first new monster. For people who don't like spiders, [[SarcasmMode rejoice!]] XANA now has a four cannon-legged behemoth that moves very much like a spider. It wipes out the group in the season 2 premiere, and is one of the signs of XANA's power increasing, a plot point that would loom over the Lyoko Warriors' heads throughout all of Season 2.
** NOW we get into the Scyphozoa, which is quite possibly put, XANA's most horrific monster and his [[TheDragon Dragon]] for Seasons 2 and 3. Unlike his other monsters, the Scyphozoa is not designed to fight. Rather, it is meant to drain Aelita's memories to allow XANA access to the [[spoiler:Keys of the Lyoko, which, if he manages to obtain, will enable him to ''escape the supercomputer'' and infect the world-wide web]]. It takes the form of a floating jellyfish, using its tentacles to subdue its victims and drain them of their memories. Aelita is subjected to it numerous times throughout the series, as is Yumi in Episode 34, and from we can tell, the experience is NOT pleasant and is very likely [[MindRape Mind raping whomever gets caught by it in order to extract data]]. To up the nightmares even further, if the thing catches you, you can't escape unless there's someone else nearby who can cut the tentacles. Why can't you escape? BECAUSE IT CAN'T DIE. Even worse, it's implied that even hitting the eye, which should normally destroy a XANA monster, WILL. NOT. KILL IT.
*** And in Season 3? When you thought that with [[spoiler:XANA's escape in the network]] means that it will never appear again? Surprise! It isn't! And in fact, it turns out to have even more functions than just data extraction! It can implant viruses in the Lyoko Warriors, viruses that XANA uses to mind control them. Yes, the Lyoko Warriors, who should be immune to XANA's mind control tactics in the virtual world... ''don't have it anymore!'' Once again, Aelita is subjected to the process so that XANA can have her delete the surface sectors in order to destroy Lyoko piece by piece. Then, in the Season 3 finale... William, the SixthRanger, falls victim to the creature. He then proceeds to [[spoiler:lead an army of Creepers on Lyoko's core, destroying it and ending up as XANA's [[TheDragon general]] for most of Season 4.]]
** XANA-William. Now under XANA's control, William has been upgraded into a dark and powerful [[TheJuggernaut juggernaut]] leading XANA's forces on Lyoko. His expressions are psychotic, and much like his master, he rarely ever talks, except to grunt and yell. He acts rather creepy around Yumi and Aelita, and he's extremely brutal in battle, to the point of the show needing to use a GoryDiscretionShot, which it has NEVER needed with XANA's other monsters.
** The monsters in the Digital Sea, partly due to them having very sharp teeth, or, in the Kalamar's case, a [[ThisIsADrill very big drill]]. Unlike XANA's other monsters, with whom devirtualization is just going back to the real world, a defeat via these creatures equals ''permanent deletion'' due to the nature of the Digital Sea.
** Finally, there's the Kolossus. It's a gigantic lava golem that looks very much like an EldritchAbomination. For reference, here it [[http://vignette4.wikia.nocookie.net/codelyoko/images/8/80/Sueurs_froides_348.jpg/revision/latest?cb=20111018190207 is]]. It only appears in three of the last four episodes of the series, but those three leave enough of an impact. It can destroy the Skidbladnir in one hit, and it has two Eyes of XANA that need to be hit in order to destroy it. Note the size of the thing. It can hold Lyoko towers in its hand. Now you can run.
* An Alternate Universe example: What if what happened to the Real Life factory in France happened in the show before Jeremie turned on the Supercomputer? That would mean that Aelita and Franz would have ''died!''
* Some of XANA's attacks do border on this, especially if it's a widespread offensive. XANA-possessed characters can be particularly creepy, and many examples of XANA trying to murder the protagonists (like ''electrocuting Jérémie'') can induce nightmares.
** Most ways that XANA tries to kill Jérémie can cause Nightmare Fuel. Jérémie gets electrocuted by one of the power sources for the ''Supercomputer'', as well as getting electrocuted by the specters.
** Also, when he discovers that the one [[spoiler:Franz Hopper]] is actually a polymorphic specter in disguise, it gets pissed at him, turns into smoke to invade his airways, and proceeds to suffocate him while Ulrich can do nothing but watch.
* A lot of the psychotic expressions XANA-fied William makes.
** Not just him actually, ''any'' xanafied person will often arbore a quite scary expression with VoiceOfTheLegion to complete.
* [[http://i56.tinypic.com/25zqc5i.jpg This lovely shot]] of a XANA-possessed Aelita.
** Want to make this concept even scarier? Watch "Ghost Channel" (where Aelita proves she's able to essentially do the same things XANA could do in the first season, and without needing the towers, could do so unopposed if she wanted to) and then imagine what she and XANA could accomplish if he was able to control her more often.
*** To add a bit more horror to this, during Season 4, it is implied several times that XANA ''does'' know of what he could accomplish if he had Aelita with him permanently, but intends to kill Hopper first before he does so. Meaning that had the final battle gone the other way around, XANA's next objective likely would've been having Aelita under his control much like William, and given how much he powered up William, one shudders to think of what upgrades Aelita would've had if XANA succeeded in such a goal.
* Jérémie scores one with the "Marabounta". Basically, sort of purple goop starts covering Lyoko, devouring initially every XANA monster, then going after the Lyoko Warriors. The heroes were definitively {{squick}}ed -- especially when it ''ate Yumi''. (Seriously, just watch the scene where she is EatenAlive by the thing. Imagine how ''she'' must have felt. You have to wonder just why these kids even do this.)
* [[EverythingsDeaderWithZombies "Attack of the Zombies"]]. The title pretty much says everything by itself.
** It really doesn't. XANA possesses Kiwi, Odd's pet dog, and uses him to spread a zombifying virus through the school. Most of the group is trapped in the cafeteria, and William is trying to keep them there (give him some credit, he doesn't know about Lyoko yet). Odd is bitten and Ulrich and William have to restrain him. Imagine seeing your best friend gagged and tied up and trying to bite you while moaning in the VoiceOfTheLegion.
** The worst part? Thanks to LoopholeAbuse, this doesn't counts as [=XANAfying=], meaning that ''the Lyoko Warriors are not immune to this one''.
** Jeremie gets bitten before Aelita deactivates the tower and has a horrifying transformation. He can barely gasp out 'Return to the Past now!' and his voice is already ''changing''... if Aelita had been seconds late...
* Of course, in animation there's a ''lot'' of ArtEvolution between pilot episodes and the resulting series themselves, but ''Garage Kids'' (in certain scenes) combines OffModel and UncannyValley and turns them UpToEleven. To clarify: Ulrich's avatar has eyes that seem like they came from the first ''VideoGame/CrashBandicoot1996''. But still, TropesAreNotBad (see WhatCouldHaveBeen in the [[Trivia/CodeLyoko Trivia tab]]).
** Not to mention the darker tone the pilot has a whole. Each scene of virus activity from Xanadu is given a real sense of dread, and the rather unclear boundary concerning the virtual and real worlds has its own slew of horrors. In fact, given how the show creators at the time were taking influence from '''Anime/SerialExperimentsLain''' (A series which is filled with nightmare fuel and whose head writer worked on Anime/DigimonTamers, which has it's own brand of horrors), one can start to understand where all the nightmare fuel on this page could come from... and then wonder just ''how bad'' it could've gone had the pilot concept been used!
* "Killer Music" borders on the High Octane variety. Imagine an [=MP3=] becoming a successful hit. Now imagine it being [[SingleStanzaSong a simple, looped sentence]] (I've seen the Italian version and it was like, "Uh, hah, you will never win") creepily reminiscent of synthethizeritis. ''[[OhCrap Now picture it putting each of its listeners in a comatose state.]]'' It's especially terrifying when Odd falls victim to it, as he's stuck with a huge grin on his face, thus looking like he'd been murdered by ComicBook/TheJoker.
* Who else [[BowelBreakingBricks shat bricks]] when we saw [[spoiler:XANA's disguise of Jérémie breaking down]] from "Ghost Channel"? XANA Jérémie's "[[LogicBomb NOT LOGICAL! NOT LOGICAL!]]" after the kids decide that he's the fake Jérémie because he doesn't understand that Jérémie ''would'' virtualize himself to save his friends. And then the scene where he screams and then tries to kill the characters.
-->'''XANA:''' [[EvilLaugh HAHAHAHAHAHAHAHAHAH]]! [[VoiceOfTheLegion YOU ARE GOING TO DIE]]!!!
** Let's admit it, Ghost Channel was the '''scariest''' episode of [[WesternAnimation/CodeLyoko Code Lyoko's]] first season. For a season with episodes that were mostly {{Filler}} and that involved XANA attacking and the team having to deactivate a tower in [[{{Cyberspace}} Lyoko]] (and that were pretty creepy on their own), it really drove home '''what''' kind of a threat this nutcase of a computerized OmnicidalManiac was, to the point where his [[BringMyBrownPants pants-browningly]] horrifying OneWingedAngel form at the climax now serves as the page image. [[WhamEpisode Good Lord]].
** The most terrifying thing about this episode? This was the only time XANA ever personally appeared, so we actually see that yes, ''he does take pleasure in the misery he causes''
* There are also the attacks where XANA [[AttackOfTheKillerWhatever takes over animals and uses them to attack Kadic]]. So far, we got wasps, rats, birds, boar, ''wolves''... the latter even had a scene with Ulrich falling in the middle of said wolves, who immediately start to attack him. The Return to the Past barely saves him.
* The time XANA took control of a dangerous criminal.
** In the episode with the above criminal, just how casually Jeremie informs Ulrich (via cell phone) that after he replaces the Supercomputer's nuclear core, XANA [[spoiler: is going to kill him.]] [[TroublingUnchildlikeBehavior No 12-year-old should be that calm in that situation.]]
** Potentially even worse, XANA has a noticeable sadistic streak. When there isn't obvious pressure to keep him pragmatic he's been shown to take his sweet time killing, maiming, or destroying whatever he so chooses to. There is a very real chance that Jeremy wouldn't have ever been found or would have been found in several hundred pieces by the time XANA was done.
** Slight but also very real, XANA forced this career criminal to steal a damn radioactive power source that doesn't seem to have any shielding. The whole factory, that career criminal, Jeremy after he got kidnapped, and the entire path that they took to get to the factory. Probably contaminated now with at least some radiation.
* Just how quickly Odd and Yumi deteriorate in "Ultimatum" due to being LockedInAFreezer. Yumi starts shivering first and by the time XANA has gotten tired of waiting for Aelita to give herself up, is reduced to being barely able to stand and weakly crying Odd's name as XANA prepares to kill him.
** And then there's the added idea that Odd might have accidentally caused XANA's later attack of creating an ''obscenely'' cold blizzard by telling XANA that cold is lethal to humans.
** Fun fact, this is the second time XANA ever unambiguously communicates with the heroes. He sends them a text message, simply saying to deliver Aelita to the Scyphozoa within a certain time, else, he'll kill Odd and Yumi. No theatrics like other cartoon villains. Here's the message: cold, simple, and to the point:
-->'''XANA:''' Aelita at two o'clock to give herself up to the Scyphozoa. If not, Odd and Yumi will be [[NeverSayDie liquidated]]
* The Zero Gravity episode. Think about it; the evil computer virus has taken control of FREAKIN GRAVITY to the point where it can just LAUNCH PEOPLE INTO ORBIT WITH EASE.
* The amount of times Ulrich has nearly died in general. No child would be perfectly fine with that, not even mentioning how many of them were different e.g. burned alive/dehydrated to a dangerous degree, crushed, frozen, mauled to death etc.
** The others don't escape either considering Yumi and Odd both nearly froze (Yumi ''twice''), Yumi shared the SaunaOfDeath event and Jeremie, Yumi and Odd all nearly drowned at least once each.
*** Odd's drowning is particularly disturbing since it [[LuredIntoATrap involved him taking the bait when XANA pretended to be a girl asking him to meet in the woods]]. It would appear that Odd's parents' hands off raising method severely hampered his ability to remember stranger danger.
** Every member of the group has been electrocuted at least once. ''Everyone.'' And it's not PlayedForLaughs, ever.
* In the second-to-last episode, the group decides not to send William to Lyoko since he just got freed from XANA's influence. XANA decides to make them regret that decision, and immediately possesses William's body again, prompting Yumi to devirtualize herself and fend him off to protect Jeremie. What follows is the most [[NoHoldsBarredBeatdown brutal]] [[CurbStompBattle beatdown]] ever seen in the real world. She gets launched, stalked, and toyed with for several minutes. It's hard to watch, and it isn't played for laughs.
** Ulrich gets in on it after his devirtualization and though he gets some progress against William, he's kicked so hard against the wall that it takes him a split second for him to cry out in pain.
** Following that, when XANA is destroyed, after he's forced from William's body (in a scene that's horror in its own right), he's left unconscious in the machinery room. Nobody bothers to pick him up and take him back to the control room. Do they dislike him that much?
* Franz Hopper. He may be the BigGood, but back when he was creating Lyoko, he was forced to use the [[GroundhogDayLoop Return to the Past]] 2546 times, living the same day over and over again. To be blunt, the process drove him [[SanitySlippage insane]]. He's quite clearly paranoid and unstable as his diary demonstrates, though thankfully, he seems to have pulled himself together in the present-day of the series.

[[folder:Novel series]]
* [[spoiler:XANA as Eva]] has determined the fastest way to get a necessary item is to [[spoiler:maim whoever has it]]. At one point, before getting on the airplane to France, she is seen with luggage, new clothing, and a computer, with no indication as to where she got any of it, except that the T-shirt is ''stained''.