When Nightmares are the MonsterOfTheWeek, you WILL have horror by the bucketful.

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* Everything the Smooze does. It's MadeOfEvil, and causes an extremely PainfulTransformation into a Nightmare when ingested.
** Some Diamond Dogs drank a small amount - not enough to cause transformation. When they died, they ''melted''.
* On that note, each nightmare the Mane cast has is made of this. It's not just the nightmare itself, but how broken they are afterwards. They're witnessing themselves betraying, torturing, and killing those closest to them, and they can't stop it.
** Pinkie's nightmare is [[spoiler: ''FanFic/{{Cupcakes}}'']].
** Twilight's nightmare is [[spoiler: ''FanFic/SeveringAndReconnection'']].
** Fluttershy's is [[spoiler: ''FanFic/{{Pattycakes}}'']].
** Zecora's is an original creation. In it, Zecora [[spoiler: boils Apple Bloom alive as she screams for help.]] Furthermore, it was ''toned down'' from the first draft [=KnightMysterio=] devised.
** Rarity's is based off of [[spoiler: the Tumblr blog Lil' Miss Rarity.]]
** Rainbow's is [[spoiler: ''FanFic/RainbowFactory'']].
* A Blank Story Part 1 and 2 [[spoiler:Zomponies! and [[AndIMustScream Grey Hoof's ultimate punishnment]]]]
** The descriptions of the [[spoiler: zomponies]] are made of Nightmare Fuel. Anyone affected suffers a PainfulTransformation as their ''[[EyeScream eyes dissolve]]'', their flesh rots, and they ''scream''. The pain is described as similar to being dipped in acid, and [[spoiler: Medic]] can feel ''wind blowing through his ribcage.''
** So much of the Blank Story arc is Nightmare Fuel. When [[spoiler: Grey Hoof]] has his VillainousBreakdown, his skeleton, and only his skeleton, grow to the size of an alicorn. He grows skeletal wings and a horn, too, and they all tear his flesh to shreds as they grow.
** Then, ''mutant centipedes as big as a pony start crawling out of his back.''
* The song from "Melody of Agony Part 1 and 2" To clarify: [[spoiler: Anyone known for their loyalty, such as Rainbow Dash, suffers tremendous terror and pain just from hearing it. When it plays again, everyone affected suffers so much agony they're forced into a coma, the song strong enough to start to affect RED Sniper in the other world. And when it plays a third time, everyone affected falls under a suggestion that they have to kill whomever or whatever they were loyal to end the pain. This creates such [[SarcasmMode delightful]] scenes such as Apple Bloom trying to kill her fellow Crusaders, Spike trying to kill Twilight Sparkle, BLU Sniper trying to kill his teammates, Mayor Mare trying to burn Ponyville down, Luna leading a second coup against Celestia, Mrs. Cake trying to murder her children while begging her husband to stop her...]]
* "Tick tick, goes the clock..." [[spoiler:Doctor Whooves' PainfulTransformation into Nightmare Doctor. Minuette/Riversong, experiencing the the last few minutes of life of every version of herself that died a horrible, agonizing death, ones that she didn't regenerate from, at the same time, on eternal repeat. Demoman experiencing every time he died and forgetting each time he survived. Applejack having to live out Pinkie's and Twilight's MindRape dreams, both as victim and victimizer.]]
* When [[spoiler: Nightmare Moon possesses the Elements she's sent nightmares to]], Pyroland starts rotting. In addition, Spy and Scout have [[spoiler: mutated into disturbing monstrous forms.]]
* [[spoiler:Slenderman,a NighInvulnerable EldritchAbomination with MindRape powers. There is nothing more that needs to be said about him. Team RED was lucky that the RED Medic was able to use ThePowerOfFriendship and Kindness (thourgh Sasha).]]
** And now, [[spoiler:the Slenderman of their world might have taken notice. [[SarcasmMode Fun times]]]]
* Nightmare Juggernaut is so large and muscular that his skin has torn open in places to reveal the muscle below. Then, he grows a minigun from his chest.
* In chapter 19, Celestia is unable to refer to Slendermane as anything other than [[spoiler: herself]], which leads to this:
--> '''Celestia''': "[[spoiler: KILL ME NO NOT ME KILL ME NO NOT ME!!]]"
* Chapter 20, Good Lord.
** The revelation that [[spoiler:''Discord'' is terrified of Slendermane.]]
** Celestia [[spoiler:being mind-controlled by Slendermane into possibly committing murder.]]
** Gray Mann's [[DealWithTheDevil deal]] with [[spoiler:this world's Slenderman.]]
** [[spoiler:Christian Brutal Sniper, the physical embodiment of Sniper's darkest fantasies and self-loathing.]]
** Nightmare Gardener, made from poor sweet and kind [[spoiler:Cheerilee.]]
*** Her transformation especially. Vine wings and a horn grow from her body, her blood turns green, and her personality is so utterly subsumed that her cutie mark alters.
* Nightmare [[spoiler: Gardener]] is made of a substance that is delicious to [[spoiler: changelings]]. While there's no question [[AssholeVictim she deserved being devoured]], it's still a pretty awful way to go.
* When [=BLU=] Engineer is [[spoiler: attacked by a Weeping Angel, both Engineers are thrown far into the past, away from any hope of rescue. When we see them again, they've [[GoMadFromTheIsolation gone mad from the isolation]] and are working for Slendermane as Nightmare Clockwork and the Vagineer.]]
* Essentially any time a [=TF2=] Freakshow appears is going to be this... unless it's [[BigLippedAlligatorMoment PAINis]] [[CrowningMomentOfFunny Cupcake]].
* Nightmare Clockwork's first act upon directly engaging the heroes is to [[spoiler: revert everyone who was a Nightmare at one point to that state. This carries over to their [=RED=] counterparts]].
* A recent chapter has [[spoiler: [[HumanoidAbomination Vagineer and Heavydile]] menacing the RED team alongside [[AxCrazy Christian Brutal Sniper]].]] To say nothing of the fact that there are now [[spoiler: [[OhCrap FIVE]] Nightmares]] facing off against the citizens of Ponyville...
* The TroubledBackstoryFlashback to Barricade and the Doctor trying to apprehend Jeff the Killer. [[spoiler: Barricade is ForcedToWatch (the Doctor's blindfolded) as Jeff slowly tortures Barricade's seven - man squad to death.]]
* When the protagonists visit Canterlot, they're [[spoiler: dragged into personalized nightmares. Some of them are quite disturbing.]]
** Princess Celestia is [[spoiler: immobilized by thorny branches, surrounded by several reminders of the murder she may have accidentally committed.]]
** [[spoiler: The Master]] shows up to torment Derpy.
** Soldier's confronted by [[spoiler: the burning corpses of his old family.]]
** Both Pinkie and Rarity face [[spoiler: an EnemyWithout from their nightmares.]]
** Medic's assaulted by [[spoiler: his past victims - over a hundred men and women.]]
* Celestia, believing that [[RedShirt a random, totally innocent guard]] is actually Slendermane, [[spoiler: dissects him methodically while he's still alive. Her SanitySlippage is becoming very apparent]].
* Imagine having your home broken into by a complete stranger. Now imagine having said stranger try to rape your mother in front of you. Her rapist also happens to be a grown man armed with a knife. You have to resort to murder to protect your mother, despite being only a child. [[spoiler: Scout's backstory]] is a whopping mixture of Nightmare Fuel, Tear Jerker, and FridgeHorror, and the worst part is that it could happen ''[[AdultFear in real life]]''.
* The Difference Between Dreams and Reality takes place in a CuckooNest that's trapped [[spoiler: all of Ponyville, save for those not native to the universe]]. It's scarily plausible.
** [[spoiler: Princess Celestia]] is a gibbering mess in the CuckooNest. Seeing how reliant on Slendermane's power the [[spoiler: BigGood]] has become is terrifying. What's even worse is that she seems almost fine in reality.