This game may have been thought to be LighterAndSofter by the graphics but [[NightmareFuel oh boy]], ''[[BloodierAndGorier they were wrong!]]''
* Female characters scream and shriek horribly as they are killed; most notably the female wizard, her voice often fades to a gurgle as her body is torn apart.
* [[spoiler:Adria's betrayal]], leading to [[spoiler:Diablo ripping apart Leah's body, possessing her remains and reconstituting her form,]] and [[spoiler:the rebirth of Diablo, the Lord of Terror himself, as the embodiment of all seven Great Evils in one being, the Prime Evil. And worse, Diablo wants to [[HellInvadesHeaven destroy the High Heavens themselves]]]]. [[HolyShitQuotient Holy Shit]] does not even begin to describe it.
** [[spoiler:The invasion of Heaven itself. The High Heavens are supposed to be a place full of holy and awesomeness, even if a lot of the angels are dicks. But when Diablo invades, you're treated to sights like angels being tortured, ugly demonic cysts that you have to destroy to continue and the place becoming more and more Hellish as you progress to the Crystal Arch. And as mentioned below, not even angels are immune to Diablo's evil!]]
** In the shoes of Lorath Nahr, this would've counted as one during Act V, [[spoiler:when they're off to confront Adria. The Nephalem were so full of anger and vengeance that it just looks like [[RevengeBeforeReason they're willing to compromise the greater goal to find out Malthael's whereabouts just so they can kill Adria.]] When reminded that they need to get Malthael's location first, their answer is cold and as Lorath commented: "Well, that doesn't sound helpful...". This means we're facing with the very possibility as Tyrael feared at the end of the game: The prospect of humanity's savior being consumed with negative thoughts that they might doom others instead.]]
* Take a moment to listen to the music of [[spoiler: Whimsyshire]] on headphones, full volume, in a dark room, and without looking at the game. [[note]]As you might have guessed, the music is actually a real musical piece being played backwards. The original piece is called ''Gaspard de la Nuit - Le Gibet'' by Ravel. [[/note]]
* The Halls of Agony in general. These were King Leoric's old torture chambers, which saw plenty of use back when he was still alive and going insane due to Diablo's attempts to possess him and the evil whisperings of his EvilChancellor Lazarus, claiming the lives of quite a lot of people, up to and including his own queen, who Lazarus manipulated Leoric into executing so he would be able to devote himself fully to turning Albrecht into a vessel for the Lord of Terror. And that was ''before'' Maghda and her coven decided to appropriate the place for their twisted rituals. What makes things even worse is reading his journal, which captures his descent from noble king to stark raving mad step by step. The Darkening was not a fun time to live through.
** To make things worse, in one of the later entries of this journal, Leoric states that [[AndIMustScream he is aware of his madness, but powerless to stop his horrific actions.]]
* The massacre of Alcarnus in Act II, though not shown onscreen, showcases quite vividly just how evil Maghda and her Coven are. These are people whose primary means of fueling their magic (even illusions) involves ColdBloodedTorture, and Maghda at this point is [[VillainousBreakdown getting desperate]].
* Ghom is a rare case of turning the BigEater trope into NightmareFuel and NauseaFuel. While you are fighting him, you can get your hands on his journal, which narrates how he forced his human prisoners into ''[[IAmAHumanitarian eating their own comrades]]'', only to eat them himself after that.
* Listen very carefully during the battle with Diablo. You can hear screaming, just high enough to hear, but not louder than the background noise. It's surprisingly creepy.
** It's even worse because [[spoiler:you know who is supplying the screaming. Poor Leah...]]
* The descriptions of some of the monsters are pure nightmare as well.
** One would expect the Tormented Stingers, for example, to be scorpion-like demons out of hell. But instead, these monsters are created by twisting the bodies of human sacrifices into these horrific forms.
** The Unburied are a hideous amalgamation of corpses flung into mass graves, animated by foul magic.
** [[ExactlyWhatItSaysOnTheTin Terror Demons]] are made from Diablo's nightmares and once drove a member of the Horadrim insane simply by appearing. Add that to the fact that their expertise are [[JumpScare ambush attacks]].
** The Skeletal Nightmares, which you fight near the end of the game in Act IV, are the ultimate fate of mortal sorcerers who summon and try to bind demons to their will, [[HoistByTheirOwnPetard only to become enslaved to the very same demonic power]]. Deckard Cain notes in his tomes that they are the ultimate proof that there can be no peace between men and demons.
** [[spoiler:Corrupted Angels]] in general, probably the perfect embodiment of [[FromBadToWorse just how bad things have gotten]] in Act IV.
** [[OurAngelsAreDifferent Malthael]] himself has become this. Originally he was The Archangel of Wisdom and the Leader of the Angiris Council but went mad sometime and now he has become the Angel of Death. [[http://www.youtube.com/watch?v=Cb7QJwQ58T0 I dare thee mortal]].
** Cain's description of the Butcher is disturbing for a completely different reason: [[spoiler:he describes the horrifying demonic Butcher'''''s'''''. That's right, there are ''more'' of them.]]
* The ''[[https://www.youtube.com/watch?v=Cb7QJwQ58T0 Reaper of Souls]]'' intro has this with Malthael, specifically when, while he's butchering the Horadrim, we get to see his powers up close when he literally ''causes a Horadrim to wither and decay, ripping his screaming, struggling soul out of his body.'' Tyrael puts it best:
-->...You should all... ''[[OhCrap run.]]''
* The first chunk of Act V, especially before you get to your first settlement. First you see a couple people running and screaming...par for the course, honestly, by now. Then you see a large group of people running, only to see their souls yanked from their bodies, turning them into Undead enemies to fight you. You progress, and are told about [[HopeSpot survivors in the church]]. You reach the church, only to see a jet of darkness burst from the doors. You hear pained screams for an instant, before they are rendered silent. Even as you play through Westmarch, you continue to see some...[[ParanoiaFuel not all, but some]] of the soldiers get their souls pulled, turning them into Revenants, too.
* When you get close to the Soul Crucibles that you need to destroy, there are dead bodies everywhere, just piled up in the streets. And you have to walk over them.
* The [[spoiler:Grand Maester]]'s plan during ''The Templar Reckoning'' quest for Kormac. [[spoiler:This utter bastard plans to implement the same horrendous [[ColdBloodedTorture initiation ritual]] that resulted in [[BrainwashedAndCrazy what happened to Kormac and Jondar]] and apply it on a grander scale, doing this to ''every citizen of Westmarch and beyond'' in order to make them Templars]]. It's little wonder that Kormac decides that [[spoiler:the Maester, and the Order itself, need to end]].
* Malthael's plan during Reaper of Souls. Tearing one Horadrim's soul out in front of Tyrael and eating it is disturbing. Seeing [[spoiler:the Soul Crucibles in Westmarch]], and the floor littered with bodies from the Reaper attack is horrifying. Then you learn from Tyrael and his fragment of the stolen Black Soulstone that [[spoiler:Malthael is planning to use the soulstone to forcibly contain all demonic essence in the plane the Soulstone is in - and he's about to send it into Sanctuary. And [[KillEmAll human souls are half-demonic.]]]] By the time you reach him, he has a LOT of souls under his control, plus [[SealedEvilInACan the Black Soulstone and its contents]]... And Malthael [[OneWingedAngel eats souls.]]
* The [[spoiler:soul crucibles]] are nasty business themselves, seeing as they can [[spoiler:rip the souls out of still-living mortals, leaving their flesh for use as Malthael's minions]]. You do manage to destroy all three [[spoiler:(the one under Kasadya's control was incomplete, and crumbled when she died)]], but the implications of how many they claimed are still very nasty. You know it's fucked up when Myriam has difficulty tolerating their existence.
-->''"Let's just say I need to see it destroyed with my own eyes if I am to ever sleep again."''
* The Perilous Cave in Act V, a [[BonusDungeon side dungeon]] that's teeming with giant maggots. Interacting with certain objects like corpses and loose stones will cause more maggots to drop from the ceiling. Oh, and there's the Maggot Broods, who spit out even more of them. [[NauseaFuel Gross!]]
* [[spoiler: The implications of Malthael's successful release of the Black Soulstone on Sanctuary. He tooled it to absorb all demons on the plane. And humans are all half demon. No one gives a clear answer to what this means, but everyone agrees that there is no way that it won't result in the death of every human on the plane.]]
** And to make matters worse? [[spoiler:All of the demonic essence that Malthael ripped out of the people he killed with that stone before he shattered it? Went straight to Diablo himself. Not only is the Prime Evil free to walk the earth again, but he's even more powerful now than he ever was before]].
* The following conversation with Eirena comes out of nowhere and isn't expanded upon either. The location at which she says it, such as King Leoric's mansion with its gruesome backstory, doesn't make things better either.
-->'''Eirena:''' There are two boys playing over there. Can you see them?\\
'''Player:''' What do you mean? There is nothing there.\\
'''Eirena:''' ''*cheerily*'' Never mind. They must be dead.
** Mixed with TearJerker - two boys playing around Leoric's manor implies she's seeing the ghosts of Aiden (The Dark Wanderer) and his younger brother Albrecht, Leoric's ''sons'', both of whom ended up as unwilling hosts to Diablo. Eirena's probably seeing some of the last happy moments that family had before everything literally went to hell.
* The [[ThePowerOfHate literally-powered-by-hatred]] Demon Hunters already look scary enough with the GlowingEyesOfDoom that come with most helms, but The Shadow's Mask, part of The Shadow's Mantle set, [[HiddenEyes hides their eyes in darkness]].
* Tyrael's [[spoiler:OhCrap realization]] at the ending of ''Reaper of Souls''. [[spoiler:The Nephalem has grown too powerful, yet still suspectible of being tempted to evil. And if they do not resist, humanity is doomed. You may want to start praying that they actually resist in the future! But seeing that it's Blizzard and their history of having a boner for FallenHero, combined with their realization that Angels can be just as bad as Demons... Maybe the Sanctuary saga has a chance [[GrandFinale to end on]] [[DownerEnding an extremely bleak note...]]]]
* The Blood Cult of the Temple of the Firstborn from the new release for Adventure Mode are singularly nasty. Aside from their usual business of sacrificing others, they have a habit of turning people into living roach hatcheries, turn themselves into demons, and choose only the choicest of victims for their rituals. [[spoiler:Knowing that they cannot take Nephalem in open combat, the cult steals upon them when they're asleep or unarmed before cutting open their veins for the blood they desire]]. And the guy running the show is [[spoiler:Vidian, the Lord of Envy and one of Azmodan's surviving Sin Lieutenants, who presumably wants the power of the Nephalem for himself]].