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Nightmare Fuel: Grimm
For people allergic to bees or insect-phobic with "Beeware". Swarming bees.
Rats showed up in a later episode. There was a few lingering shots of a corpse trapped in a locked vehicle with starved rats — the results were not pretty.
In-universe, Grimms to many Wesen. The Wesen that aren't immediately intimidated by Grimms tend to possess a large amount of physical capability.
"Lonelyhearts" is pretty much an hour of Fridge Horror if you're a woman.
Spinnetods and everything about them. The fact that they vomit acid into their victims' digestive tracts, then suck their liquified organs out through their stomachs, and the fact that it's completely instinctual, and they have no control over their murders.
In "Last Grim Standing", the returning fighters in the Wesen Fight Club are fed the losers.
In "Organ Grinder", the detectives uncover a Geier criminal operation that kidnaps homeless kids off the streets, drains their blood, cuts out their organs while they're still alive, dumps their bodies into a burning pit, and then sells the organs to other Wesen as herbal remedies. Worse yet, the criminal ring picks out their targets through their front as a pro-bono clinic for the impoverished.
The fates of those the Ogre targets in "Game Ogre".
The first Seelengut's fate in "The Good Shepherd" - dropped into a wood chipper... and all they find of him is his leg, because the metal hip he had jammed up the machine.
In "Three Coins in a Fuchsbau" Nick watches an old film reel of Nazi propaganda and sees Hitler transform into a Schakal. The effect was chilling. It is Hitler, and the man himself was pretty darn horrifying, but it's worsened by that fact that Schakale are known for kidnapping and eating babies.
Larry the Wildermann clawing at the drug pump attached to his spine enough to tear the flesh open, leaving a gaping, bloody hole in the back of his neck.
The victims of the Mauvais Dentes, a menacing sabertoothed-tiger-man who can be best described as a bit of a messy eater.
The Coyotl have a ritualistic practice of every male in the pack (most of which are probably related to the girl in question) raping their female members on the full moon following the girl's 17th birthday.
The Murciélago. AUGH. A bat-like creature with blood-red eyes whose high-pitched screams cause bleeding from all orifices, and the lovely little side effect of causing your eyeballs to explode. Behold◊! (Warning: Don't open this link at night in a dark room. Really.)
The fate of Adalind's cat, if you're a cat owner or generally a pet lover. Not made any better by Rosalie and Monroe's nonchalant response.
Hell, think of what the cat went through - put into a shelter (as an adult, so possibly it had a happy life before being abandoned), then adopted just for the reason of being drugged into becoming a weapon, then ending up (possibly) under the wheels of a car. Could cross over into tearjerker territory as well.
Or you can look at the cat from Rosalee’s perspective in that scene. You know this hyper aggressive cat is possessed by a poison that can seriously mess with people. You walk in expecting to be safe, but see that this crazy thing is strong enough to break through the carrier. Stop thinking fluffy kitty and start thinking more along the lines of deadly wild animal, or live grenade.
Also strong or hyped up on magical mojo to cling to the ceiling. Given the sorts of Zaubertrank that Hexenbiest seem to use, it's likely that the cat was dead for all intents and purposes long before that scene.
And imagine what the results would be if they did that to a dog. It would be even worse. Just think about it.
JulietteJulietteJulietteJulietteJuliette. After Renard had to kiss Juliette to break her out of a spell after drinking a potion to make himself "pure of heart", he is now starting to become obsessed with her. Episode previews even show him sneaking into her house to watch her sleep. Creepy as hell.
It doesn't help that Juliette seems to be suffering from some of it herself as she sees Nick as Renard when she goes to kiss him.
Just imagine what that poor foster-family went through in The Bottle Imp! They watched a seemingly sweet and innocent little girl suddenly become a flesh-hungry monster who bit the father's arm open (and a wound like that is going to need serious stitches!) but if they ever try to explain as much no one will ever believe them!
Or for that matter, the girl's family. At the tender age of 9, the girl attacks and almost kills her own mother and then a couple of stranger. while she shows concern for the mother, she shows very little concern about the others. Imagine seeing your own daughter turn into a raving unrepentant murderer. If not for Nick and the Löwen prison guard, there's really not a lot of ways for that story to end.
It's slightly unnerving to see Nick walk into a prison and spot angry Wesen — lots of them — mixed in with the general prison population.
After finding a pit of half-decomposed corpses underneath the house of a Wendigo, said Wendigo attacks, causing Nick to trip and end up in the pit of corpses. He fumbles in the dark, trying to find his flashlight while accidentally grabbing rotten body parts.
La Llorona's demon◊ face. Her undead children may also◊ count, and so might the fact that we never really find out anything about her (she doesn't seem to be Wesen)...
Juliette's hallucinations in "Natural Born Wesen" and "Mr. Sandman" after taking the potion.
Even more horrifying, Renard's hallucination of Juliette in his bed. It's the first time we've seen him absolutely terrified.
The Woged state of Frau Pech - think Hexenbiest-level gruesomeness Up to Eleven.
The Jinnamuru Xunte, a lovely little Wesen that blinds you by spraying a parasite into your eyes, feeds off your tears, then leaves you to die. It preys off those who are emotionally vulnerable, picking up victims at group grief-therapy sessions. Its victims may not die from the attack—but those parasites grow fast (especially in the dark; now consider that covering the eyes is often part of a normal medical treatment for severe irritation) And as if the eye thing wasn't bad enough, just seeing that tongue of his lapping at the women's faces, and that one shot where it looks like its coming at the viewer.
Oh, and once the parasites it sprays into its victims eyes are done growing? They EAT THEIR WAY OUT OF THE EYES. In this troper's opinion, that scene was one of the most disturbing and frightening things he has EVER seen on this, or ANY other tv show
Then there's the potion used to kill the parasites which involves removing the Jinnamuru Xunte's eye while its in its wesen form. Oh, and it has to be alive when the eye is taken out so if you've been infected with its parasites and the Xunte dies before you can take its eye, you've pretty much screwed.
The Volcanalis. For starters, it is not a Wesen, but a demon that lives in mountains and fries from the inside out whoever takes its "property" - their mere presence is enough to bring water to a rapid boil - usually accompanied by the mountains they inhabit EXPLODING soon afterwards - this happened to Mt. Vesuvius. In order to immobilize and kill one to save Portland, Nick, Renard and Monroe have to freeze it with liquid nitrogen, and shattering it.
But the worst part about it? Even when it was shattered, it was still alive for a few seconds.
The wesen skin/fur "tanning" trailer that our heroes find in "Endangered" and the thought of what goes on in there.
The Musai. They find artists or those with artistic capabilities and make them fall madly in love with them via a pheromone-filled kiss. And the madly part? Not a figure of speech. Those under their spell literally go crazy and end up killing the Musai's former lovers, getting locked up in an institution, committing suicide, or a combination of the three. In fact according to one of the Grimm journals it was a Musai that made Van Gogh cut off his ear. And from what we see of one they don't appear to feel too guilty about it.
The Cracher-Mortal. One day, you're going around minding your business and then some guy walks up to you and just spits in your face. Before you can even complain about the sheer nastiness of the ordeal, you're under his spell and more likely to wake up in a morgue or something. If you do wake up, that is.
To make it even worse the process is explicitly described as being excruciatingly painful.
Nick as a zombie. He's deathly pale, has bloodshot eyes, may or may not have tears of blood and if he sees you, he might BEAT YOU TO DEATH.
The effects of the mushroom a Bauerschwein chef was using to poison Blutbaden. It painfully bloats their stomach and compels them to climb up into a tree just in time for their stomach to explode.
The process of "cutting" a female naiad, which involves forcing her into a woge, and then using a knife to cut the webbing between their toes and fingers, forcing them to be Brought Down to Normal. The connotations in the episode "One Night Stand" also bring up images of Rape as Drama.
Adalind rubbing magical gore on her pregnant stomach without a single shred of remorse. It's worse that the gore takes shapes such as a skull and a spider before being absorbed into her body. Not knowing what exactly it's doing to her child makes it even worse.
Gregorek, the Gelumcaedus, who starts out as a simple thief... but progresses to murder by throwing a guy around the room before biting his arm off with such force that there is blood spatter on the ceiling. It gets worse from there - he rips off a guy's leg and attempts to do the same to Nick, who is thankfully able to stop him.
The fate of Renko, who tried to kill a Koschei... Talk about Body Horror.
There's also the quick flash of the baby's face turning into a wide-mouthed skull... Still thinking getting your powers back was a good idea, Adalind?
Same episode, the monster of the week tracks down anyone he deems to be a "great warrior" (so cops and military) fights them to the death, and if he thinks they "are worthy" he scalps them, tans said scalp, and sews it into a coat made of human scalps for him to wear.