* CompleteMonster: [[EldritchAbomination Nightmare]], the BigBad, she should be AboveGoodAndEvil. However, the sheer amount of enjoyment she gets out of her actions (which are usually KickTheDog at best and which tend to be done purely ForTheEvulz) puts her straight into this territory. Not only did she [[DemonicPossession possess]] Princess Luna (turning her into Nightmare Moon) and create Discord (making her responsible for everything he did as well), she's also implied to be [[TheManBehindTheMan behind]] several of the monster attacks on Ponyville in canon and is the reason Celestia and Luna are the [[LastOfHisKind last two alicorns]]. And all that's before the story even starts; in the story itself, she kidnaps the Mane Cast's pets as bait for Fluttershy, who she then takes as her new host body ([[AndIMustScream trapping the poor filly in her own mind]]), before brainwashing and transforming the aforementioned pets into monsters as part of her army. When she realizes that Zecora followed Fluttershy and witnessed the possession, she has her minions hunt her down to stop her from telling anyone- and after she's captured Zecora, she tortures her before releasing her to hunted again for fun. She then launches an attack on Ponyville that claims the lives of [[spoiler: Princess Celestia, Ditzy Doo, Rainbow Dash, and Princess Luna]], with her personally killing the latter two. After the rest of the Mane Cast have been forced to flee, Nightmare proceeds to [[ImAHumanitarian eat]] most of Ponyville, before locking the survivors in a cage made from the bones of her victims'and leaving them to die as she [[KillItWithFire sets the town on fire]]-except Sweetie Bell, who Nightmare takes prisoner to use as a hostage/bargaining chip against Rarity and the others. All of this happens within the first five chapters of the story.
* HilariousInHindsight: Twilight being groomed to be a successor for the princesses rings pretty closely to the ending of the third season of the series, [[spoiler: where she does get crowned a princess of Equestria and becomes an Alicorn]]. [[TearJerker Too bad Raefire wasn't around to see this happen.]]
* MoralEventHorizon:
** Literally ''everything'' Nightmare does is either this or a KickTheDog moment.
** Discord apparently crossed it in the backstory, when he killed Celestia and Luna's parents -- he {{Mind Rape}}d them so far past the DespairEventHorizon that they simply lost the will to live and wasted away.
* NeverLiveItDown: In a humorous moment shortly before everything goes to hell, Twilight is shown worrying that this will happen in regards to her breakdown in "Lesson Zero".
* {{Tearjerker}}: In real life, the author's untimely passing.
* TheWoobie: Several.
** Birostris Oswaft - being TheLastOfHisKind for ''ten thousand years'' [[{{Understatement}} definitely left a mark on him]], so much so that he asks Twilight to [[MercyKill kill him and put him out of his misery]].