* CompleteMonster:
** ''Voices''' "An Apple A Day": [[EvilOldFolks Old Bill Cole]] is the CrankyNeighbor of Tim Barrett's grandmother and turns out to be hiding a truly horrific secret. After Tim gets too close to his prized apple orchard, Cole furiously reprimands him and his grandmother, going so far as to taunt them over Tim's missing grandfather. When Tim vandalizes his orchard in revenge, he eats one of the apples, only to discover he is [[MutagenicFood slowly mutating]] into [[{{Transflormation}} an apple tree]]. When Tim goes to Cole's desperate for answers, he discovers far too late that the old man's orchard is made up of dozens of poor souls who ingested his apples, among them [[WouldHurtAChild many other children]], as well as his grandfather. Cole than watches with a cruel smile as the boy transforms into the newest addition to his orchard.
** ''The Whisperer'''s "Gabriel": [[OurDemonsAreDifferent Gabriel]] is a handsome, brooding student who Samantha initially suspects of being a vampire. [[ActuallyNotAVampire In truth]], he is an ancient, [[SoulEating soul-eating]] demon who claims to be feared even by vampires, and uses his [[BitchInSheepsClothing friendly persona]] to lure the girl into his clutches. As Gabriel feeds on Samantha, she glimpses the millions of souls Gabriel has consumed over the years, [[AndIMustScream all trapped in the demon's body and writhing in eternal agony]].
** ''Dream Demon'''s "Carnival Dance": [[Myth/MayanMythology Ah Puch]], the wicked [[EverybodyHatesHades God of Death]], demanded HumanSacrifice and tried to slaughter the Mayan civilization before he was banished by the other Gods. Centuries later, Ah Puch [[DemonicPossession possesses]] a young man through an antique mask he ordered for a parade and enslaves his friend, forcing the boy to become a puppet for his own amusement and [[KickTheDog kill several of the birds he loves]]. Ah Puch soon reveals himself at the parade as he gleefully draws "the Breath of Life" from the hundreds of people attending before moving onto ravage the world again.
* ParanoiaFuel: Almost every story contains a healthy dosage of paranoia fuel.
** [[spoiler:Is your babysitter acting strangely because she's moody or because she's been replaced with a doppelgänger? Is that little girl who's been hanging around you lately just lonely or is she hiding something more sinister? And do the people you're babysitting for not want you to check on the baby because they're afraid she'll wake up or are they really only using that as a coverup for something that's not quite natural?]]
* WhatDoYouMeanItsForKids: With a far [[DarkerAndEdgier darker, violent atmosphere]] genuinely likable characters dying horrifically, sadistic endings, and horrific fates befalling children, ''The Midnight Library'' is considerably more dark and cruel than you'd expect of more renowned works like Literature/{{Goosebumps}} or Series/AreYouAfraidOfTheDark.
* TheWoobie: Almost all the protagonists, whether they're nice kids or not. Some who ''really'' need a hug are Kate Openshaw from ''Voices'', Tim Barnett from ''An Apple A Day'', Chloe from ''The Cat Lady'', Jessica from ''Liar Liar'', and Liam from ''Blind Witness''.
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