[[caption-width-right:350:''I am a monument to all your sins.'']]
-->''"We exist together now. Two corpses in one grave..."''
-->--'''The Gravemind'''


[[folder:Halo: Combat Evolved]]
* Everything Flood-related, especially the first encounter with them in the level 343 Guilty Spark, which is loaded with creepy. See BleakLevel on the main page.
** The downed Pelican ("We're under attack by an unknown enemy! It isn't Covenant!"). The abandoned artillery pieces all facing away from you. The Grunts that used to flee at the mere sight of you run right into your killzone in a panicked retreat from something ''even scarier''. Strange shadows and noises seems to follow you through the trees. "Allies" appears on the HUD, only to disappear almost immediately without any trace. You follow the trail of carnage into a vast, underground complex, all painted in Covenant blood and deserted save for one man, a wounded Marine so insane with terror that he can't tell friend from foe. You wander deeper and deeper into the ancient ruin and finally find what's left of the rest of his unit. You download the feed from one unfortunate soldier's helmet camera, watch the entire squad get slaughtered...and then your radar goes wild. Even Master Chief looked briefly disturbed after watching the video feed.
** And the thing is is that their introduction was a total surprise. There had been no signs in the instruction manual or anything in the game that indicated that it was going to turn into a horror movie. Yes, the Grunts were running away, but that could have been from anything. Everyone remembers when they first walked into the last room and suddenly a bunch of red dots appear on their radar, and then these jellyfish appear out of nowhere and start jumping at the screen.
* The Infection Forms seem to bounce off your shields, causing only minimal damage. A burst from the assault rifle can take down a lot of them at once. Surely the Flood are only a true threat for unarmored Marines, not a Mjolnir-equipped supersoldier like you. This is going to be easy. Then the Combat Forms show up...
* Bungie recently had an article that talked about the creative origin of the Flood. Upon being shown a single still picture of just one Flood form, the ESRB demanded the game be given an M-Rating. And that's without the lovely things mentioned above.
* The Flood music themes. Features Ominous EtherealChoir, PsychoStrings, and {{Scare Chord}}s. Special mentions go to "Suite Autumn", "Shadows", the ambient section of the "Truth and Reconciliation Suite", and "Library Suite".
** You thought the original Flood themes were scary? The ''Anniversary'' remixes turn the nightmare dial UpToEleven: [[http://www.youtube.com/watch?v=njqFybTtD8I "Between Beams (Shadows)"]], [[http://www.youtube.com/watch?v=d_PXQFuNbNM "In the Substance of It" (not on the original OST)]], "Bad Dream (Trace Amounts)", [[http://www.youtube.com/watch?v=VcXJbton40w "Dewey Decimate (Library Suite)"]], "Demons and Heretics (Devils, Monsters)", [[http://www.youtube.com/watch?v=Dtl5IvMZ6NM "Unfortunate Discovery (What Once was Lost)"]] (now sounds like a Music/SunnO [[DroneOfDread drone doom]] piece) , "Xenoarcheology (Alien Corridors)" and [[http://www.youtube.com/watch?v=wM2Qd-Ij6VI "Fragments"]].
* Pvt. Jenkins, who got overran by the Flood and remained conscious after transformation! In the second book, he made attempts to throw himself into harm's way, but as luck would have it, he ended up being the ''only'' Flood form they captured alive for study. Throughout the book, his mind and the Flood's mind are battling it out.
* Captain Keyes' fate, getting turned into an immobile mass of flesh, only to get the sweet release of death when Master Chief burns him.
** According to the second book, he was slowly losing all his memories as the parasite took over. Towards the end, he was struggling to remember his own name! Furthermore, if you'd been around five minutes quicker, you'd be able to save him.
** Not only that, but in the game, [[spoiler:at the start of that particular level, you start RIGHT OUTSIDE the room he's in, but of course you need to do the rest of the level first.]] Just take a peek through those grates to the right...
** In Halo: Anniversary, under him, there's a terminal containing his last moments from his point of view. He's repeating his serial number, and they're rifling though his memories...We see Miranda and Dr. Halsey, and those memories are being stolen, and he knows it, and his voice keeps switching between normal and Flood-toned. And then at the end, he swears, "You will not have me." And then the Flood speak again, and ''now it's the Gravemind'': '''"We already do."'''
* Regarding non-Flood examples, pretty much all the aliens in the series look frightening in some way, whether they actually look scary like the Jackals or are just scary to fight against like the Hunters. It's made even worse in the first game by the fact that half the time you're in dim corridors and it's incredibly quiet, because of the suspense. Some more examples include:
** The Grunts. Yes, you heard right. They look really vicious without their mask, and we've all had at least one time where a Grunt saw us without knowing it and shrieked, causing us to jump. Fiends.
** The Elites (especially camouflaged Zealots) when they roar or when they're right next to you and you bump into them.
** The Hunters have no actual limbs. They're comprised of a bunch of worm-like things (1.4 meters) called Lekgolo that come together under their armor. In later games, they also make up the Scarabs.
*** The encounter with Hunters in The Silent Cartographer deserves a special mention. It starts with being dropped on to the beach by a Pelican, surrounded by allies, as you storm through countless easy Covenant enemies and enjoy the pretty scenery around you. You even get a Warthog halfway through, making the level even easier than it already is. But wait, the trees up ahead look too dense to drive through, so you begrudgingly leave your allies behind and head forward, figuring that if it was easy so far, what's the worse that could be up ahead? Suddenly, you come upon a clearing, and in it are two, huge, lumbering, armor-plated aliens making loud groaning and roaring sounds in the distance. Though intimidated slightly, you step forward, figuring that they probably can't be as tough as they look, only to have them shoot a series of explosive green blasts at you. You try to close the distance a bit and hope that melee will be a bit more effective, only to fly several feet forward after realizing that one of them has hit you from behind. The next one then charges at you like a roaring, alien freight train, and swings its massive arm at you, killing you in an instant.
*** In Truth and Reconciliation, two of them drop down from the gravlift while ominous music plays. At night. It's arguably worse. To make it even worse, the encounter on Truth and Reconciliation makes them seem unstoppable if it's your first time playing through a Halo game. Anyone who played Halo: CE as their first Halo game knows the sheer terror that pair brought upon you, cutting through all of your troops like they were nothing, deflecting sniper rifle bullets straight off of them, and grenades only making them flinch. However, the horror is slightly deflated when you eventually discover that a single pistol shot to their weak spot (their back) takes them out.
* Think of Master Chief from the Covenant's perspective. He's just one soldier, but he is perfectly capable of picking off entire squads one by one until every last fighter is dead and then move on to repeat the process ad infinitum.
* ''Type-33 Guided Munitions Launcher'', more infamously known as the '''Needler''', is basically a terror weapon incarnate. Homing crystalline spikes that not only embed themselves in your flesh but also explode, breaking bones, displacing organs and tissue, further dispersing tiny flechettes of crystal in and near the wound and commonly to nearby people. If hit by multiple shards, you are as good as dead, but just one is incredibly dangerous.
* The entire purpose of the Halo array and the way it's slowly unveiled to you. At first, Halo is just presented as a mysterious megastructure. There's hints that it was built by the Forerunners, but its true purpose is unknown. Then you encounter the Flood. Along comes Guilty Spark, who explains that Halo is a weapon designed to destroy The Flood. All well and good right? Then, just as you're about to activate Halo, Cortana explains its ''true'' function: [[spoiler: Halo doesn't kill The Flood, ''it kills anything The Flood can infect.'' Each of the 7 Halo rings can emit a destructive pulse that wipes out just about all sentient life within a 25,000 light year radius. Because the Forerunners figured that the only way to stop The Flood was to starve them to death, and the only way to do that is to ''kill an entire Galaxy.'' And as Halo 2 points out, the entire Covenant religion is based upon ''deliberately activating the rings.'']]
** One of the terminals in Halo: CE Anniversary has a (soon to be rampant) 343 Guilty Spark lament about how alone he is on Halo, guarding a weapon that has no target...which he says he could tune to ''any'' target.

[[folder:Halo 2]]
* The Gravemind is a particularly frightening being that truly lives up to being a EldritchAbomination, thanks to VoiceOfTheLegion and its creepy competency at delivering [[BreakingSpeech breaking speeches]] and corrupting people to evil. Its appearance, particularly its graphically updated one pictured above, doesn't exactly help matters either. Plus, there's no telling where those awful tentacles will pop up next...
** Oh, and one of those tentacles? The Prophet of Regret is ''melded'' to one of them, still completely conscious and clearly in great pain. There's no answer for why the Gravemind would do such a thing other than [[ForTheEvulz "He can."]]
** ''This is not your grave...*incomprehensible gurgle*...but you are welcome in it.''
** The HD Gravemind has another detail that makes him worse than his original graphics. In the original, the impression that the Gravemind gave was that of a vast Venus Flytrap-esque beast. Look closer at the HD Gravemind when he talks, specifically at the back of his throat. That's a giant fanged ''maw'' with brief flashes of what looks like an organic meat grinder of teeth in its gullet. The way it's animated makes it look like it's in a perpetual SlasherSmile as well.
** In the original game, the animations made it look like Arbiter was struggling against it's grip and at least gaining some ground if not enough. The anniversary edition and it's improved animations makes it clear that the Gravemind is just ''toying'' with the Arbiter, twisting and turning him at its leisure. It says incredible things that Arbiter manages to keep his NervesOfSteel when he's being held ''very'' close to the Gravemind's horrible maw.
* The hidden messages in the game. In Halo 2's soundtrack, we have ''Mausoleum Suite'', a song that plays during the intro cutscene of the ''The Arbiter'' and during the confrontation with Tartarus in ''The Great Journey''. In this track, a voice can be heard in the background. At first, it seems intelligible, but play the song in reverse, and you get this: http://www.youtube.com/watch?v=CBdAAyXEmJg. Fans like to speculate that this is Mendicant Bias.
* Much like the first game, the soundtrack itself offers many terrifying tunes:
** The middle section [[http://www.youtube.com/watch?v=Ara1HO6CbpE (Infected)]] of "Mausoleum Suite". It starts out with slow jungle drums and spooky moaning voices (similar to the Shadow Temple music from ''VideoGame/TheLegendOfZeldaOcarinaOfTime'') and then turns into a cacophony of synthesizer effects with guttural voices that seem to be reversed speech but are really just gibberish.
** Another scary one is "Ancient Machine", a [[Series/TheTwilightZone Twilight Zone]]-like melody with organic Flood noises and vocals similar to the aforementioned "Infected".
** The second section of "[[https://www.youtube.com/watch?v=tsZAtqEzC24 Librarian's Gift]]" from ''Halo 2: Anniversary'' heard on The Oracle after the elevator ride (replacing the second half of the aforementioned "Infected") will give you recurring Flood nightmares for a long time to come.
** The music playing during the level "The Oracle" that has distorted reversed voices (during the battle between the Heretics and the Flood in the lab).
* When you kill a Brute, [[JumpScare you may see his eyes twitch]].

[[folder:Halo 3]]
* Contrasting the previous games, now the Marines (as well as Elites and Brutes) can be [[FaceFullOfAlienWingWong "Floodiefied"]] in realtime. Yes, they turn them into Flood in your face, with a touch of BodyHorror, not to mention that if you manage to shoot an infected soldier in a way that doesn't make it explode and walk up to its body, you can see one clinging to the spine...
** "[[https://www.youtube.com/watch?v=d1zWeaVZpsM Hunted]]". Talk about NothingIsScarier.
* Perhaps the creepiest parts in the game are when the Flood start ''talking'' to you. Hearing the Gravemind cursing and taunting you as his minions swarm you from every direction is ''chilling.''
* From the level Floodgate, the insane Marine considering suicide adds to the horrific atmosphere, much like the psychotic Marine in the first game.
** [[http://halo.wikia.com/wiki/AWOL_Marine Same]] voice actor for [[http://halo.wikia.com/wiki/Suicidal_Marine both]]. That guy is ''disturbing'' in-character.
** One line that the suicidal Marine said gives a [[BodyHorror good description]] of an infected person: "I could see it crawling, SLIDING AROUND BENEATH THEIR SKIN!"
** When the game was released, technology had finally allowed for the realtime conversion of Elites, Brutes, and Marines into Flood forms. It's creepy enough when an Infection Form jams its way into a corpse...but it's way worse when they manage to infect a still-living target.
* Cortana has been captured and tortured. She has something that the Gravemind wants, and he will take it by force. As an AI, Cortana can't be raped in the traditional sense, but the UnfortunateImplications are still very much there.
** The Halo Evolutions story Human Weakness shows exactly what the Gravemind did to Cortana, and [[SchmuckBait it's not as bad as you think...]]it's much, much worse.
* And here's this fun little message from the Gravemind if you listen to the Flood theme backwards: "Side by side, we march as one. Humans and Elites will die. The Earth will fall if we strike together. So forth shall all life."
* Browsing the terminals in the game. Between the lack of noise in many areas you find them in, the odd "swooping" sounds as you interact with them, the random alarm prompts and the oddly incoherent messages based around the apocalypse of the Forerunners and talking about the death of millions in many cases, it all adds together into a NothingIsScarier form of creepiness.
** "I SEE YOU RECLAIMER." Even more creepier than you realize that the one who sent those words was [[spoiler:Mendicant Bias, the Forerunner A.I. who betrayed his masters for the Flood, which caused the first activation of the Halos]]. [[spoiler:The final (Legendary) Terminal is almost [[SugarWiki/HeartwarmingMoments heartwarming]], though.]]
* Much like the previous games, the soundtrack has a few choice moments:
** First, we have ''Dread Intrusion'' played during the level ''Floodgate''. It starts off in the typical, already-creepy Flood themes but soon adds [[SubliminalSeduction back-masked speech]] from the Gravemind. Play it in reverse, and you get this: http://www.youtube.com/watch?v=YspMcFfCmZA. The middle segment is an almost-heroic sounding drum but reminiscent of "Ghosts of Reach" from the Halo 2 soundtrack, but when it gets to the pause, instead of returning with doubled-up awesome, you hear a strange wailing screech come in, and it returns to creepy ambiance music.
** In the level ''The Covenant'', when the Flood shows up, the song ''Black Tower'' is played. Again, a voice is heard. Play it backwards and be treated to this: http://www.youtube.com/watch?v=RH39l43pWGw. This appears to be a reference to T.S. Elliot's poem ''The Hollow Men''.
* Possibly Gravemind's creepiest line in any game. After Truth dies and Gravemind betrays you, massive tentacles burst up from beneath the platform the Chief and the Arbiter are on. This is then followed by insane, diseased laughter, followed by this:
--> '''Gravemind''': Now the gate has been unlatched, headstones pushed aside...corpses shift and offer room...''a fate you must abide!''
* The level ''Cortana''. There's a ''reason'' that's the least-played level!
** For those who don't know, this level is the one where you essentially break into the Flood's house in order to rescue Cortana. The "house" was originally a spaceship, but almost every wall, floor, and ceiling is covered in "Flood matter," which turn out to be oozing, infected pustules that spew enemies when shot. It's kind of like the halls of an insect hive. The Flood will attack from all sides (including up) as you try to navigate this somewhat-nightmarish landscape. It doesn't help that the level is somewhat confusing; many players get turned around easily even after several playthroughs. As you fight through it, you get to listen to Cortana's tortured, disjointed rantings and Gravemind's apocalyptic proclamations. Nearly all of Cortana's transmissions are either outright skin-crawling in their delivery, if not outright terrifying, with some carrying threatening tones in her voice.
** What's worse is that as the level progresses, Cortana's transmissions become more and more frantic and confusing, eventually becoming incoherent and horrific screams of pain...before she suddenly starts speaking in a lifeless monotone. Not only that, at that point, her graphics turn from blue to green. Also, the Gravemind moments become more and more "insane evil genocide monster."
*** ''"We exist together now. Two corpses in one grave"''.
*** ''A collection of lies, that's all I am! Stolen thoughts and memories!''
*** ''"Gravemind: (intrigued) "And yet, perhaps a part of her...remains?" (maniacal laughter, fades into ''Cortana's'' maniacal laughter). Her laughter is really unsettling.
*** ''"It was THE COIN'S FAULT! I wanted to KEEP YOU SAFE! Make you STRONG!"'' Made a ''thousand'' times creepier if you've read ''The Fall of Reach'' and know the significance of that transmission.
*** ''This is UNSC AI Serial Number CTN 0452-9. I am a monument to all your sins.''
** The background noise heard throughout the level, especially considering that the noises being made aren't made by any Flood forms you encounter, leaving what horrors could be found on High Charity up to one's imagination.
* [[spoiler:343 Guilty Spark]] having a complete mental breakdown in the last level and going through a rampancy. It's very scary to see such an affable, if slightly annoying, character completely turning 180 and becoming an extremely dangerous foe who has lost his mind. Before it, you don't expect him to be a harmful threat, but then he proves you wrong ''big time'' by [[spoiler:killing Johnson]] and burning the Master Chief. When you fight him, nothing works. Grenades, pistol, machine-guns, sniper rifles, plasma guns, anti-tank weapons - none of them work. The only thing you can do is make him snap even further, and pretty soon you start feeling your heart pumping from desperation alone. [[RedEyesTakeWarning The red eye works, too, for the fear factor]].

[[folder:Halo Reach]]
* You haven't seen a Hunter in action until you've seen a pair use those damn Assault Cannons (essentially ''semi-auto'' high-explosive rocket launchers with BottomlessMagazines) to wipe out more than 15 friendly Marines in [[CurbStompBattle less than 10 seconds]] during "Tip of the Spear" in ''VideoGame/HaloReach'' [[note]]If you take out the AA gun before killing the hunters, they're still around when a Pelican airdrops reinforcements.[[/note]]. You duck behind a rock, reload your assault rifle, and when you come back into action, ''every last Marine'' which just got dropped from that Pelican is gone in a horrible subversion of TheCavalry.
* This game introduces a new piece of wildlife called the Gúta that could give the Flood a run for its money. Think of a [[VideoGame/{{Fallout}} Deathclaw]] but with elongated features. They are actually capable of killing entire ''squads'' of Elites, which are still feared at this point. The kicker? You encounter these things at [[DarknessEqualsDeath night]].

[[folder:Halo 4]]
* Some of Cortana's [[spoiler:rampant screaming]]. For instance, this line scares people:
-->'''Cortana:''' I will NOT. ALLOW YOU. To LEAVE THIS PLANET!
** This line may also give you chills.
-->'''Cortana:''' Do you know what that condescending bitch said to me after our first game of chess?!
*** To put it in perspective, she's talking about Halsey, her "mother." The words she said to her after the game were '"Quando il gioco è finito, il re e il pedone vanno nella stessa scatola. [[note]] Translated from Italian to English: When the game is over, the king and the pawn go in the same box.[[/note]]
** One of Cortana's lines in the level "Composer": [[spoiler:Why should we save them?]] It's like something out of Dead Space.
* Promethean Knights. Their helmets opens up to a glowing skull, which screams at you. [[spoiler: Worse, they are made of the victims of the Composer. [[HarsherInHindsight Definitely makes that skull look more terrifying...]]]]
* The Composer must be powered by NightmareFuel because it is positively ''oozing'' horror:
** [[spoiler:Chief and Cortana are too late to stop the Didact from taking it, unable to keep him from firing it, and then get the horrifying image of the people around them on Ivanoff Station disintegrating in ashes. And not instantaneously. ''WE SEE THEIR SKIN PEEL OFF THEIR BONES.'' You're even "treated" to a close look at its effects on Doctor Sandra Tillson.]]
** [[spoiler: Worse, they weren't killed by the process at all, [[AndIMustScream which means they had felt the tremendous pain as their skin was being peeled apart from their flesh and their bodies]] ''[[AndIMustScream disintegrating]]'' [[AndIMustScream and still presumably felt the pain as they were cataloged by the Composer to later be turned into Promethean Knights and the sort by Didact to replace their dwindling ranks as Chief tore through their numbers]].]]
** Even worse, [[spoiler:essentially, the Composer fatally digitizes people. Cortana is a digital lifeform. She's in shock afterward because she could hear the digitally fragmented minds/souls of the people, screaming in pain and terror. No wonder she was [[HeroicBSOD blue-screening]] when the Chief came to.]]
---> '''Cortana''': "I was monitoring the data feeds. [[spoiler:I could ''hear'' them...what was ''left'' of them...]]"
** [[spoiler: The Chief and Cortana are unable to prevent the Didact from firing it twice. The second time, it's on Earth, and the affected area in New Phoenix is still quarantined six months later.]]
** [[spoiler:The people of New Phoenix were commonly believed to have received a MercyKill when Chief destroyed the Composer, but Episode 5 of Spartan Ops reveals that their memories were somehow transported to Requiem and transformed into Promethans...Spartan Thorn could be fighting his friends and family out there.]]
** A throwaway line in ''Literature/HaloSilentium'' will leave you with [[FridgeHorror endless horror once you realize the implications.]] [[spoiler: When taking the personalities of humans defeated at Charum Hakkor, the Ecumene Council gave the Warrior-Servants and Lifeworkers "Composers"...as in ''plural''. That's right, folks. The Forerunners built ''more than one Composer!'' Every horrific thing you just read about the Composer? ''It could all happen again''...]]
*** Confirmed to be true in ''ComicBook/HaloEscalation'' Issue 9: [[spoiler:The Didact is alive and operating from the Composer's Forge, where the Composers were built. He has ''six'' fully operational Composers. Fortunately, he seems to no longer want to Compose humanity. Unfortunately, he has since decided ''[[OOCIsSeriousBusiness he would rather use a Halo on Earth]]'']].
** [[spoiler: The Ur-Didact's fate in ''ComicBook/HaloEscalation'' issue 10.]] Part of Installation 03 along with [[spoiler:the Ur-Didact]] is dropped onto the Composer's Forge, causing all five Composers at nearby to detonate with [[spoiler:the Ur-Didact seemingly disintegrating and ending up composed.]] However, WordOfGod has stated that [[spoiler:he]] has not been completely composed in the way that is usually known due to the destruction of the Composers and [[spoiler:the Ur-Didact's]] resistance to the Composer mentioned in the terminals in ''VideoGame/Halo4''. What exactly happened to [[spoiler:him]] [[NothingIsScarier has not yet been revealed]] and [[spoiler:the last shot of him was his glowing remains]]. All that is known is that [[spoiler:he]] is still alive and will likely return to the narrative at some point.
* The cutscene for Spartan Ops Episode 2 has Dr. Glassman being sucked up by a Forerunner artifact, complete with Capt. Lasky futilely trying to save him. With how his body breaks into glowing orangle particles just before he gets pulled in, it looks disturbingly like he's being Composed.
** Episode 3 [[spoiler:reveals Glassman's fate. On the plus side, he hasn't been composed. On the minus side, he's been captured by the Covenant, and apparently is offering to trade information for his life; with Jul 'Mdama suggesting he'll end up RewardedAsATraitorDeserves after helping them. Also, the Artifact is apparently accessing systems aboard the Infinity, gathering information and transmitting it to Requiem.]]
* Episode 5 shows that the Promethean Majestic Squad are fighting are not ancient humans, but the victims from the New Phoenix incident six months before. Thorne said he knew people there. He would have been "killing" his friends and family... ''again and again and again''.
** I'm pretty sure its just once per person. Its kind of hard to restore data after its contain has been blown apart by a half dozen 8-gauge shotgun shells. Still quite disturbing, though.
*** It's not only entirely possible for Knights to come back after their body is destroyed, it's the entire ''purpose'' of the Promethean Watchers. Which adds an entirely new urgency to killing Watchers in gameplay: not only do they bring enemies back, they're bringing back those same people who composed ''again and again and again...''
* Episode 6, Chapter 5 has Crimson sent in after [[spoiler: another Spartan team, Switchback, needed help taking down a Harvester guarded by Covenant and Prometheans. When Crimson arrives, all that is found are Switchback's removed IFF tags, nothing else. No clues are given to what exactly happened to them. The fact that the IFF tags were removed seem to indicate that they were captured. For what purpose? Likely nothing good.]]
** [[spoiler:Becomes NightmareRetardant when it's shown that they were just captured, and only the leader was killed.]]
* Episode 7 in general. The Infinity is attacked by Covenant and Prometheans.
* The Flood combat in the War Games. Especially on a dark map, like Shatter. [[NothingIsScarier You're just looking around, watching fo-]][[JumpScare WHAT THE HELL WAS THAT?!]]
** Doesn't help that the Flood can use Armor Abilities as well. Seeing a Flood rocket towards you using it's thruster pack is nerve racking. Especially if your CQC aim is bad.
*** Also, the Flood models themselves. Look at one close up, and you'll see what I mean.
*** Specifically, [[spoiler: you're looking at the first-ever ''Spartan'' Combat-Forms.]] Thank god they're just based on speculation as far as canon is concerned.
* Imagine being Roland when Halsey activates the former's override. Chances are, he won't want to hear the phrase "undid iridium" ever again.
* [[spoiler:Halsey's severed arm in the Spartan Ops epilogue.]]

[[folder:Halo 4: Forward Unto Dawn]]
* The ''entire'' Covenant attack on Corbulo Academy. Even for hardened fans of the series who have gotten used to the Covenant presence in the franchise will probably be utterly terrified of them here, since A) the attack is at night B) it's completely a surprise and they kill [[spoiler:everyone at the Academy besides Lasky, Orenski, and Sully]], C) it's at the very start of the war, so nobody knows ''what in the hell'' they're being attacked by, and D) the entire attack is seen through the eyes of undertrained teenage cadets.
* The screams of people [[spoiler:falling from a destroyed Space Elevator]]. There's some very appropriately squishy sound effects to go along with the impact. [[NotTheFallThatKillsYou To think the ones killed by plasma fire were the]] ''[[NotTheFallThatKillsYou lucky ones]]''.
** [[spoiler:Dimah was last seen on the Space Elevator. One of the falling bodies is wearing an all-white uniform.]]
* The Elite slicing the statue in half at the end of Episode 3.
** In that same note, Cortana's [[Literature/TheLordOfTheRings Gollum]] -esque "arguments" with her [[spoiler:rampant mind]] in the episode's teaser:
--> '''Cortana''' ''(shrill, demonic voice)'': ''I hate you!''
--> ''(as glowing sphere flashes bright red and distorts, unusually high-pitched voice, shocked)'': ''Cortana!''
-->''(shrill, demonic voice)'': '''''STOP IT!'''''
--> ''(normal Cortana voice)'' I've made up my mind. ''(young girl's voice)'' If I'm going to die aboard this ship, ''then Chief will suffer the same fate as me!''
--> ''(Elderly woman's voice)'': Cortana, ''control yourself!''
--> ''(young woman's voice)'': ''I've'' sacrificed ''everything'' for '''''him!'''''
* [[spoiler:Unlike in the games, where Elite's cloaking has a semi-visible distortion effect a la the Predator, in FUD, it's completely invisible. J.J.'s death is a illustrates how terrifying this is, as he literally walks into an Elite without seeing it.]]
* In Episode 4, [[spoiler: the cadets ask why the Chief came to save them; he responds that they were the last people still alive. The cadets are surprised that they're the sole survivors of the Academy, but Chief corrects them; they're the last surviving people ''on the planet''.]]
* John-117, the Master Chief, a seven-foot tall cyborg and a striding force of death and destruction is only [[spoiler:fifteen years old in 2526. Meaning he's barely old enough to have a driver's license. Meaning he's even ''younger'' than the frightened cadets he's saving from certain death at the hands of monstrous, alien zealots.]] The fact he does this all with an almost robotic calm makes the human cost of the Spartan-II project seem that much more horrible.
** Reinforced in the end of episode 5. [[spoiler:The surviving cadets are aboard a Pelican with John-117, Fred-104, and Kelly-087. Kelly and Fred take off their helmets (They look at the Chief, who keeps his on and looks away), leaving the cadet surprised at how young they look, leading to this exchange:]]
-->'''Sully''': [[spoiler:How old are all of you?]]
-->'''Kelly''': [[spoiler:That's classified.]]
* Episode 4 shows just how messy a supercombine can be. [[spoiler:Colonel Mehaffy was damn near liquified.]]

[[folder:Halo 5: Guardians]]
* The Legendary ending. [[spoiler:Rogue!Cortana has ''a [[TheEndOfTheWorldAsWeKnowIt Halo]]''.]]
* It's hard to say which is worse: [[spoiler:Cortana is still rampant, or she's ''not'' rampant and just [[WithGreatPowerComesGreatInsanity mad with power]]. Either way, when she shows her true nature to Fireteam Osiris, her ranting and sneering is just ''chilling''. Even worse is that she's utterly convinced she's in the right, that the Spartan-IV's and their kind deserve to ''die'' and that Chief will agree with her when she wakes him from stasis in 10,000 years.]]
* The ''Argent Moon'', the derelict ship of the eponymous second mission that Blue Team is sent to recover from Covenant forces. At first, you could be forgiven for thinking that the Covenant found it and killed everyone aboard. But it turns out the ''Moon'' was already a GhostShip long before Kig-Yar scouts stumbled upon it. ONI scientists had been working on an airborne bioweapon, and it somehow got loose. The result, as hinted by numerous dessicated corpses with an odd residue beneath them, was everyone aboard the entire vessel dying horrifically. According to a record by the shipboard AI, those who were at ground zero for the containment breach (who died instantly as their soft tissues ''liquefied'' as a result) were "the lucky ones."
* Hearing the Jackals [[AliensSpeakingEnglish speak English]] for the first time in the franchise is a little jarring.
* There's an EasterEgg on the multiplayer map "Rig". While the trigger for it is simple [[labelnote:*]] After GroundPound-ing a platform in the BottomlessPit in the middle of the map, you shoot two cores coming out of their silos, on the edge of the map.[[/labelnote]], the result isn't. [[spoiler: You hear [[HellIsThatNoise a piercing screech]] as a rig on the horizon is suddenly lifted from below by '''''[[AttackOfThe50FootWhatever a titanic]] [[PrecisionFStrike fucking]] SandWorm that makes Literature/{{Dune}}'s sandworms look like maggots.]]''''' One can only hope that no one was on that rig.

[[folder:Halo Wars]]
* Flood maps in Halo Wars occasionally have what sounds very much like someone shrieking, "HELP ME!" as a random background noise.
** The level Shield World sometimes has one of the Marines complain that he was bitten or scratched (by the Flood) and is starting to feel strange...
* The recent E3 trailer for ''Halo Wars 2'' revealed a terrifying new secret for the game and the series in general. [[spoiler:The Flood are back.]]
** The excellently rendered, [[SarcasmMode beautiful]] [[spoiler:Brute Combat Form seen when the Flood return for the first time]].
** The utterly gigantic [[spoiler:Proto-Gravemind tentacles]].

[[folder:The Forerunner Saga]]
* The Precursors. Once driven by an obsession to create life, [[spoiler: they were nearly wiped out by one of their creations, the Forerunners. They are '''''not''''' happy about it and deliver a terrifying message to the Forerunners:]]
-->'''[[spoiler: Gravemind/Precursor]]''': Our urge to create is immutable; we ''must'' create. But the beings we create shall never again reach out in strength against us. All that is created will ''suffer''. All will be born in suffering, endless grayness shall be their lot. All creation will tailor to failure and pain, that ''never again'' shall the offspring of the eternal Fount rise up against their creators. Listen to the silence. Ten million years of deep silence. And now, whimpers and cries; not of birth. That is what we bring: a great crushing weight to press down youth and hope. No more ''will''. No more freedom. Nothing new but agonizing death and never good shall come of it. ''[[MeaningfulEcho We are the last of those who gave you breath and form, millions of years ago. We are the last of those your kind defied and ruthlessly destroyed. We are the last Precursors.]]'' ''[[AscendedToAHigherPlaneOfExistence And now we are]] '' '''[[IAmLegion Legion.]]'''
* [[spoiler: The Librarian, leading an expedition to a nearby galaxy, finds a primitive society of Forerunners seeded on a planet millions of years ago. A recognizable Forerunner race inhabits the planet, but at close examination, it turns out that ''everything'' on the planet was once Forerunner. Every animal and plant. The team observes a herd of cattle with many recognizable Forerunner features. Imagine living on a planet where everything, from the grass you stand on to the animals you eat, is descended from people no different from you.]]
* The Flood gains new levels of nightmare in this trilogy. Apparently, before they were the twisted space zombies [[BlatantLies we all know and love]], it was simply a dust which genetically altered certain animals and spread benignly via consumption. Eventually, it spread to humans, subtly altering their behavior, until, when it became a widely known problem, it didn't bother concealing its nature. The first incarnations that encountered humanity spread by forcing uninfected humans to consume infected humans forced to grow to horrendous sizes. To quote a description of how it was spread:
--> "Infected individuals combined their resources to force other humans to become infected- usually by cannibalism of a sacrificial individual, induced to grow to prodigious size before being consumed while still alive."
** What it did to some Forerunners was closer to the version seen in the games, though more horrific. One variation was basically dozens of Forerunners mashed together into a huge snake...centipede-beast...''thing'', complete with scales grown over their skin which moved using dozens of limbs stuck in its side, blobs of flesh with faces and limbs protruding, [[AndIMustScream some still conscious]], a twisted face melted into the thing's chest.
* A new classification of Flood was identified in the later years of the Forerunner-Flood War: the Key Mind. In short, a Gravemind created from an ''entire planet's ecosystem''.
* In addition to the graphic descriptions and chilling implications, the Flood's ability to corrupt is shown to extend far beyond mere biological matter.
** The Flood's ability to subvert A.I.s was hinted at via Cortana and Mendicant Bias in Halo 3, but this ability was taken to its logical extreme when warring against the Forerunners, who were hit with a full on ''logic plague''. Essentially, the Flood was able to dominate and enslave A.I.s and non-sapient data even faster than biological beings, and since the Forerunners utilized ancillas in almost every aspect of their lives, everything they relied upon started to betray them even before the Flood attacked. Imagine an evolving, self-aware computer virus that doesn't just corrupt data but turns it ''actively malevolent''.
--> Judicial Network has been compromised, attempting ''THERE IS PEACE IN SUBMISSION.'' --- Do not access judicial network! '''Do not access!'''
--> All Forerunner judicial proceedings are now on hold. [[TheEndOfTheWorldAsWeKnowIt All Forerunner culture is now on hold]].
* Near the end of the war, when the infestation was at its zenith, [[HyperspaceIsAScaryPlace faster-than-light travel became phenomenally dangerous]], as [[SufficientlyAdvancedAlien slip-space was being deliberately altered by the Flood to better serve their interests]]. The Flood essentially ''[[OhCrap infested hyperspace!]]''
* [[spoiler:The Ur-Didact's fate. He was trapped in that Cryptum of his for 100,000 years, and because the Domain was destroyed (something which ruined the Librarian's plan when she put him in stasis), [[GoMadFromTheIsolation he was left all alone, with only his madness for company]]. No wonder he's ruthless and genocidal by the time John frees him.]]
* [[spoiler: The true relationship between the the Forerunner, Humans, and Precursors. They did indeed reject Forerunners for the Mantle and intended for humans to hold it. The Forerunners did not accept this and drove the Precursors from the galaxy and beyond. Some Precursors survived by going dormant, others became powder that could regenerate their old selves in time, but time rendered it defective and it only created sickness and disease. The Precursors vowed that none of their creations would rise against them again and that all life would suffer and be in perpetual agony, through their new form as the Flood.]]

* ''Broken Circle'' gives us a [[SarcasmMode delightful]] example in the Gravitational Refinement Device. ArtificialGravity, selectively taken UpToEleven as a means of torture. The device can [[SquashedFlat flatten the flesh and bone in a limb]]. The blood is either forced out [[HighPressureBlood away from the victim]] or can be moved up the body, [[LudicrousGibs into untargeted areas.]]
* Certain aspects of the Hunt the Truth ARG. Halo usually is one of the few franchises that doesn't portray highly unethical SuperSoldier programs as anything but terrible due to the immense success of the Spartans and all the good they've done. Journalist Ben Jiraud blows the lid off the entire program that ONI has covered up for decades. He describes in horrifying detail what it would be like to be a sentient clone with the mind of a child with the soul purpose of dying, all of this so the families of the kidnapped Spartans-to-be would think their children were actually dead.