[[caption-width-right:333:Say hello to The Husk, one of the new bosses in ''Wrath of the Lamb''!]]
->We don't have high octane nightmare fuel [sic] on this one.
->Simply saying "ALL OF IT" will suffice.
-->-A troper on the discussion page.
Indeed, for a game whose basic premise is a mother trying to kill her son, ''The Binding of Isaac'' is pretty unsettling.
However, a lot of the game's horror can count as Tear Jerker. Isaac is abused and destitute, always unloved, always hated, in a house with an overly religious -- and also homicidally, sociopathically insane -- mother who hears voices. Oh, and the gateway to the Underworld is underneath his house filled with undead or otherwise demonic abominations of all kinds, that also adds a little bit to it.
* The designs for bosses in Wrath of the Lamb are horrifying. The new bosses seem to be the old ones... After you killed them. Most of them look absolutely horrible, [[UrineTrouble Peep]] looks the worst by far. He seems to have collapsed on the inside and [[EyeScream is bleeding from his eyesockets.]] [[http://images.wikia.com/bindingofisaac/images/2/2c/564076255.jpg Here is the poster.]]
* The freakin' trailer. If the enemies looked creepy in 2D, imagine how horrifying they are in 3D! Or, don't imagine anything and just see it for yourself... [[http://www.youtube.com/watch?v=9au_e0im0aM If you dare.]]
** The teaser for the remake is even worse - now everything is not only 3D, but creepy, rubbery puppets: [[http://www.youtube.com/watch?v=p22Sj-Zllwk Link Here]]. Their use of a photorealistic cat's head for Guppy's severed head is jarring and somehow adds a surreal edge to the horror.
** And now we have [[https://www.youtube.com/watch?v=1aBb0M8HRCQ&channel=nicalisinc the very NSFW release date trailer]] for Rebirth. Sweet dreams!
* [[IronicNurseryTune The tune that plays on the credits]] after [[spoiler:defeating the true form of Womb's / Utero's boss]]. [[WhamEpisode It comes as a great surprise]] because [[BGMOverride it replaces the BGM that usually plays on that sequence]]... And it's creepy as hell! Made worse by the fact that it's called "Jesus Loves Me." And some speculate that [[WildMassGuessing it's Isaac who sings it before]] [[spoiler:suffocating in the Chest!]]
* The Halloween update included a new level, Sheol. Which, to quote TheOtherWiki, is: "The earliest conception of the afterlife in the Jewish scriptures. [[TheNothingAfterDeath A place of darkness to which all dead go, regardless of the moral choices made in life]], and where they are 'removed from the light of God'". You know, [[UpToEleven just in case this game wasn't dark enough!]]
** A Trailer for the Sheol update [[http://www.youtube.com/watch?v=jruTNX0U3tM has been released]], and yes, it is [[DealWithTheDevil exactly]] [[DemonHead as]] [[EyeScream horrific]] as you'd expect it to be.
* The secret boss of the Halloween update. [[spoiler:What appears to be the Headless Horseman, represented as a jawless rotted head charging about the screen while its body acts like the second phase of Pestilence.]]
* The TrueFinalBoss of Sheol simply ''smiles'' before fighting you. It's unnerving.
** What's worse is his nonsensical battle cries, which for the most part are distorted demonic speech that can't quite be understood... but other times, can be clearly discerned as Isaac's name. [[FridgeHorror Why does the Devil know Isaac by name?]]
*** It's actually Mom's lines, reversed. [[Film/InTheMouthOfMadness Which has certain implications...]]
* The fight against Mom, in particular her repeated calls of "Iiii-saac..."
* ??? / Bluebaby is implied to be [[spoiler:Isaac after having locked himself in a treasure chest during [[HeroicBSOD a psychotic episode]].]]
* Similarly: ??? / Bluebaby is speculated by fans to be [[spoiler:Isaac or one of his siblings that died before birth and as a result is [[http://en.wikipedia.org/wiki/Stillbirth stillborn]], hence the X'd out eyes and the blue appearance. "Blue baby" refers to the fact that it never took its first breath and is just a lifeless corpse roaming around, which is why he has soul hearts instead of regular health. ''He was never alive to have a beating heart in the first place...'']]
* The "shopkeeper", a dried-out, eyeless corpse hanging by his neck from a rope, which would imply he committed suicide.
** That sure still doesn't stop him from taking the pennies off you whenever you buy something. [[AFateWorseThanDeath Maybe he is unable to die altogether...]]
*** If that's true, then what about the times where he ''[[BodyHorror lacks a head]]?''
*** Additional ParanoiaFuel -- note the fact that when you fight Greed, he has a noose around his neck -- one of these cadaverous shopkeepers got so mad or bored that he cut himself down and now wants to kill his customers. Now think that any single one of those shopkeepers could be him before you enter...
*** Take note of where you fight him. In secret rooms... and in shops.
* Imagine your head being slowly transformed into a tumorous mass filled with flies, all while still conscious. You'll want to put those poor Mulligans and Hives out of their misery as quickly as possible.
** And The Wrath of the Lamb? [[spoiler:Has ''an upgrade that turns you into one.'']]
** Also from Wrath of the Lamb - The ones that have bombs painfully wedged into their skull and forced to charge at the player. Just imagine it for a second - Imagine you got possessed and used as a completely unwilling ActionBomb.
* It is implied that a lot of the monsters are Isaac's lost siblings. How the hell did they end up so horribly disfigured and WHY are they there?
** Well, considering the things that appear [[spoiler:IN HIS MOTHER'S WOMB]] and in the general areas of the basement: maggots, mutated flies, what is most likely a nest of aggressive parasites, the devil, evil arcana, blood all over the place, Isaac's mother, the karaken, a daedric prince, and randomly appearing flames, it seems likely that Isaac was either the firstborn and other kids came after the problems, or Isaac is just as tough as the person who defeated a knife wielding maniac with no weapons.
*** Considering the large amount of Devilish upgrades he gets, he might as well turn up to become TheAntichrist.
**** And when you fail to become TheAntichrist -read: you die- it's possible that Isaac turns into [[AndThenJohnWasAZombie one more of them.]]
**** But, amusingly enough, Isaac is capable of taking on multiple Devilsh upgrades and multiple [[LightEmUp Holy upgrades]]... [[YinYangBomb at the same time.]]
** WordOfGod is that the monsters aren't Isaac's siblings, but Isaac ''himself''. Somehow this is ''worse.''
* Not even the game's soundtrack is immune to NightmareFuel, even if it does often cross into CrowningMusicOfAwesome. But probably the biggest offender so far would have to be [[http://www.youtube.com/watch?v=tiRhF5xc9eY Apostate.]] If anything, this track just goes to show you [[NothingIsScarier how really alone you are.]] It also doesn't help that [[spoiler:this is the theme to [[BodyHorror Mom's]] [[WombLevel womb.]]]]
* Many of the items Isaac can collect are extremely useful, but many carry a high cost in BodyHorror or [[DealWithTheDevil life energy/soul.]] Some of the worst are actually the most useful:
** The Book Of Belial: Grants Isaac increased power when used at the cost of giving him an angry EyelessFace and upside down cross mark on his forehead. [[TearsOfBlood Oh, and his tears are turned into blood.]]
** Toothpicks: Isaac uses them to [[EyeScream prop open his eyes by sticking them under his eyelids.]] [[TearsOfBlood This also causes his tears to become bloody.]]
** The Parasite: An aggressive parasite gives Isaac a split shot effect by [[BodyHorror burrowing deep into the back of his skull.]] It also dyes his tears a [[NauseaFuel sickly orangish brown.]]
** Spirit Of The Night: Gives Isaac the power of flight and ghost tears by transforming him from a little boy into a [[NightmareFace demonic specter with pale white eyes.]] [[DealWithTheDevil It doesn't help that this is also a devil room item.]]
** Stem Cells: Increases Isaac's health by [[BodyHorror growing a (probably dead) fetus on the side of his face.]]
** Cancer: A trinket that makes Isaac cry harder (shoot tears faster)... [[ExactlyWhatItSaysOnTheTin because it gives him cancer!]]
** Ouija Board: Gives Isaac ghost tears, but makes his [[NightmareFace face deathly white with a twisted expression]] like it stole his soul or something...
*** The wiki even says ''"Makes Isaac's head look undead or soulless."''
** The Pinking Shears: This is a giant pair of scissors which, upon use, makes a horrific slashing noise and ''slices off your head'', which you then control, flying it around and crying as normal as your body walks around as a little ally NPC.
* Most of the [[GameBreakingBug bugs]] of the game just fiddle with mook and boss behaviour, or lock you out of certain things. Some other bugs, however, are genuinely terrifying. One of the most persistent bugs happens after clearing a level, when, [[spoiler:after the game apparently freezing, replaces the bad dream intermission scene with a version completely in black and white, a la SinCity]]. Guaranteed to make you defecate bricks the first time you see it. Even more disturbingly still, no one really knows if it is a bug, an intentional feature, or [[ThrowItIn both]].
** Glitched Isaac. Before it was fixed, it could pop up after blowing up a blue rock. It's a copy of Isaac, riding a pony, inside of a Book of Shadows's shield. It floated around the room, and its body contorted and spun at lighting speeds while [[ExorcistHead its head stared constantly at the camera]]. And besides that, it did [[NothingIsScarier absolutely nothing]].
* In many of the secret rooms that you either find randomly from an explosive enemy or through a power-up, you'll find a single, desiccating corpse with a fly or two. In front of the corpse is sometimes a pile of coins, sometimes another power-up, but all the corpse does is sit there, rotting. Did he die from being walled up in Mom's basement? Is he the remains of one of Isaac's attempts at escape? What's worse, sometimes the corpse has no face.
** Since he looks similar to the shopkeeper (sans noose) and since you fight greed in the shops and in the secret rooms, the person sitting in the secret rooms is speculated to be the shopkeeper/ greed, if not yet another version of Isaac himself.
* There's a new boss in [[spoiler:The Womb/Utero]] called Teratoma. Wait, what does Teratoma me- [[http://en.wikipedia.org/wiki/Teratoma OH, SOMEONE TAKE IT AWAY!]]
** For those who don't want to follow the link, a teratoma is a tumor ''with teeth, eyes, arms, legs, and maybe even internal organs.'' Oh, and they're generally there from birth. [[spoiler:And the Teratoma is in the Womb...]]
*** Also? The Teratoma in Isaac is '''FILLED WITH SPIDERS.''' Think about that.
* The advert for the "Rebirth" expansion serves up Nightmare fuel hand over fist, what with the distorted music, flashing staticky backgrounds, masked nude figures and reverb-y, demonic-sounding singing.
* The new song for Sheol... is [[https://www.youtube.com/watch?v=DbiblpG4lAs this.]] It is fucking '' '''DEMONIC.''' ''
* Rebirth brings us this [[SarcasmMode beautiful thing]], [[spoiler:[[http://hydra-media.cursecdn.com/bindingofisaacrebirth.gamepedia.com/d/d4/The_Lamb_intro.png The Lamb.]]]] ''Just look at it!''
* From The Depths onward, occasionally you may hear Mom laughing from somewhere within the area. You'll then be assaulted by a pair of disembodied hands, presumably belonging to her, [[TheLegendOfZelda Wallmaster style.]]
* The spinning disembodied heads in [[spoiler:the Womb]]. They're a ''crying face orbiting around a lump of meat that slowly edges towards you.''
* [[spoiler:Isaac transforming into a demon]] in the final ending sounds awesome, right? ''[[NightmareFuel It's]] [[DownerEnding not]]''.
* End2 in ''Rebirth'' shows Isaac finding the Rubber Cement... [[spoiler:and then he turns to the camera, with his eyes a horrifying milky white, as a ScareChord plays]].
* In ''Rebirth'', pretty much '''everything about End 16!''' [[spoiler: That breathing will haunt you for life...]]