History NightmareFuel / FiendFolio

* A enemy first encountered in the Depths, the Sleeper provides the page image, and for a DAMN good reason. At first, they are a seemingly benign ghost that just floats mostly in place... until it is hit. Upon being attacked, the spectre morphs into a nightmarish figure with tiny, wild eyes, a CheshireCatGrin (that [[NestedMouths hides a mouth within it]]), and long, thin arms ending in claws, with its transformation being finished with a [[HellIsThatNoise hellish screech]]. After this, it stalks the player as a border of static surrounds them. After hitting Isaac, the figure screeches once more before departing, coating the area in darkness as it does for a few seconds. Doesn't help that the Sleeper is often placed in areas as traps, pressuring the player as they complete puzzles or defeat other enemies in the rooms it's in, creating a very tense situation.

[[caption-width-right:350:Yeah, You BETTER be scared, Isaac.[[note]]Image by slayxc2 from https://youtu.be/GIgOwBKzchE[[/note]]]]

** Not just that, it will also [[HorrorHunger eat other enemies, and sometimes the ground]] [[RhymesOnADime when there are no more around]].
** Worse still, if there are any Incisors in the room with it, it will not eat them, and instead will eat the Leper Flash they spawn, with the Incisors more than happy to give it to them. [[ItCanThink The implications of this are unsettling, to say the least.]]

** Even worse, their old designs dipped straight into the UncannyValley, with them resembling huge humanlike corpses with gaping toothless maws and pus-filled stomachs.

** Worse still, if there are any Incisors in the room with it, it will not eat them, and instead will eat the Leper Flash they spawn, With the Incisors more than happy to give it to them. [[ItCanThink The implications of this are unsettling, to say the least.]]

** The Nailhead is a Frowning Gaper variant [[ExactlyWhatItSaysOnTheTin whose head is covered in nails]], they act normal until they get close to Isaac, which causes [[YourHeadAsplode their heads explode]], scattering nails all over the ground, and also revealing their exposed brains. Ouch...
** The Contestant on the other hand, also initally act normal, some of them having giant screws lodged in their heads. The Screw-faced ones can lauch their screws as an attack, which causes their heads to cave in. But they don't necessarily aim at Isaac, they aim at '''Other Contestants''', [[NotMakingThisUpDisclaimer Yes, you read that right]], they are perfectly fine with brutally injuring each other in order to kill you.

* Also in the Corpse, there's a chance of [[MonsterWhale fighting Whales]], arguably the scariest non-boss enemy in the game rivaled only by the Sleeper. It's bad enough they are rotting corpses, but not only are they [[BossInMookClothing among the tankiest normal enemies in the game]], but they have an attack where their bellies will rupture and spews out their digestive tract! These guts will then start to shoot waving acidic tears in a triangle-shaped range while the whale corpse still try to home in on you. Destroying it first will cause the whale to collapse and its head to rupture, releasing maggots in a disgusting manner. They are proof that sometimes, it's the most realistic enemies that are the scariest.
** Even worse, their old designs dipped straight into the UncannyValley, with them resembling huge humanlike corpses with gaping toothless maws and pus filled stomachs.

* Also in the Corpse, there's a chance of [[MonsterWhale fighting Whales]], arguably the scariest non-boss enemy in the game rivaled only by the Sleeper. It's bad enough they are rotting corpses, but not only are they [[BossInMookClothing among the tankiest normal enemies in the game]], but they have an attack where their bellies will rupture and spews out their digestive tract! These guts will then start to shoot waving acidic tears in a triangle shaped range while the whale corpse still try to home in on you. Destroying it first will cause the whale to collapse and its head to rupture, releasing maggots in a disgusting manner. They are proof that sometimes, it's the most realistic enemies that are the scariest.

* Also in the Corpse, there's a chance of [[MonsterWhale fighting Whales]], arguably the scariest non-boss enemy in the game rivaled only by the Sleeper. It's bad enough they are rotting corpses, but not only are they [[BossInMookClothing among the tankiest normal enemies in the game]], but they have an attack where their bellies will rupture and spews out their digestive tract! These guts will then start to shoot waving acidic tears in a v-shaped range while the whale corpse still try to home in on you. Destroying it first will cause the whale to collapse and its head to rupture, releasing maggots in a disgusting manner. They are proof that sometimes, it's the most realistic enemies that are the scariest.
** Even worse, their old designs dipped straight into the UncannyValley, with their huge toothless maws and pus filled stomachs, which are [[BodyHorror scary in their own right]]

** Even worse, their old designs dipped straight into the UncannyValley, with their hige toothless maws and pus filled stomachs, which are [[BodyHorror scary in their own right]]

While Fiend Folio is no stranger to terrifying monsters, The Womb levels have plenty of them, especiallyin the Scarred Womb and Corpse:

* The Incisor is a floating [[BodyHorror Fistuloid-like spider]] that rips out chunks of the ground using a tube like mouth, spawning Leper Flesh. It's one of the more tame examples on this list, but still.

* Also in the Corpse, there's a chance of [[MonsterWhale fighting Whales]], arguably the scariest non-boss enemy in the game rivaled only by the Sleeper. It's bad enough they are rotting corpses, but not only are they [[BossInMookClothing among the tankiest normal enemies in the game]], but they have an attack where their bellies will rupture and spews out their digestive tract! These guts will then start to shoot waving acidic tears in a y-shaped range while the whale corpse still try to home in on you. Destroying it first will cause the whale to collapse and its head to rupture, releasing maggots in a disgusting manner. They are proof that sometimes, it's the most realistic enemies that are the scariest.

* Depending on who you ask, Mag Gapers can be quite scary, as they chase you down very quickly, breaking rocks in their path, all while having an unchanging large grin on their face, implying they enjoy their purpose in life.

* While the Mausoleum isn't the most welcoming level in the game, at least you don't have to worry about any unwelcome guests after clearing a room, right? Well, if you are playing the game after Version 2.7, your solitude would be unfortunately interrupted. Emerging from a hole in the floor, the Temptress enemy is a ghoulish, worm-like being with fleshy slits where its eyes would be, a permanent grin, and plenty of homicidal intent. After appearing, the Temptress chases Isaac across the room at an increasingly fast pace, only stopping to slam its fists into the floor or shoot rings of blood. It doesn't even lay down and die upon being defeated, as its [[YourHeadAsplode head explodes]] for a final attack.