Whether or not it's due to the game being about the ocean's pollution or being a Soulsborne game, there is a lot of nightmare fuel to go around.

Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.

• In itself, the fact that your introduction to this game includes Kril getting his shell taken by being violently thrown around in the Loan Shark's mouth should tell you what kinda game you are in for.
  • There's also the context in which this is in: Kril asks first when he's being knocked by the Loan Shark to go away because he thinks it's a bird. Kril is using his shell to defend against the birds, not unlike real Hermit Crabs. His literal only defense was taken away. We should not need to go into what this parallels in real life.
• Some may know: Many fish and related ocean-dwellers, when their eyes become fully black, usually means they are dead. Knowing this fact, your first combat encounter looks like you're being attacked by Zombie Crabs, especially since more of them keep popping up out of the sand around you as you flee. It doesn't help the fact that the actual reason may be worse depending on how you see it, Kril can't defend himself, and the music.
  • Furthermore, you can later encounter polluted hermit crabs that can be inhabiting shells you try to swap with. Not only is that a nasty surprise, but you're essentially getting a look at what could happen to Kril if he ever succumbed to the Gunk.
• The Gunk itself qualifies since it not only damages its surroundings, it corrupts those exposed to it and spreads at a rapid pace. One trip to the Moon Snail's cave, and Fort Slacktide goes from pristine and colorful to greyed out with hazardous puddles of Gunk and the inhabitants gone mad.
  • There’s also the implication that Gunk isn’t just corrupting, it’s making you go mad from the revelation that everything you know is worthless, that these treasures are just trash to some other higher being (humans). That’s a Cosmic Horror staple.
• Your currency is... microplastics. If you understand how plastics harm sea animals... this becomes pretty morbid. Especially since stat upgrades come from purging Kril of them. And don't forget that killing enemies nets you microplastics. And one of the loading screen messages reminds you that you have "microplastics in your blood". This lets you put two and two together as to where all those microplastics you're getting are coming from...
• And speaking of plastics, you will be constantly reminded of all the trash in the ocean. Because it is everywhere. It reminds you just how grim the ocean actually currently is, and how these creatures don't really understand where it came from or why it's there (at least at the start of the game). Get used to it, because it will ONLY get worse.
• Not only do you find microplastics every time you defeat an enemy—bosses and certain enemies are carrying Umami crystals, giving their eyes a bright violet glow. This carries the implication that Umami is not exclusive to Kril and his two masters, though the polluted sea creatures appear incapable of using the power properly. At least until you get to The Drain.
• Trash Day. The nightmare fuel comes from the fact that we know that it's just a bunch of garbage tossed into the sea, drifting over their settlement, but to them, it's like some gift from the gods, without knowing that it is also very likely hurting them.
• Just how fast Inkerton is to point his gun at Kril for saying he's going to find the treasure. No wonder everyone folded so quickly to Roland if you can get mortally threatened for trying to rise above the specific economic position you're in! Only everyone else being unwittingly encouraged by Kril's declaration saved him by having Roland realize killing Kril right there would make the young hermit crab a martyr.
• The Bobbit worms. Run into a spot where they’re hiding underground and boom! Kril is in the grasp of a giant worm bursting out of the sand screaming bloody murder while the worm lets out a bloodcurdling roar that more sounds like something out of a horror film. Thankfully, most are marked by a small X in the sand, but it's easy to miss if you're absorbed in combat or exploration, and some aren't telegraphed at all. And there's an area in the west of The Sands Between that's stuffed to the gills with them, and braving it is the only way to acquire the useful bobbit trap adaptation, which thankfully lets you turn this on your enemies.
  • Just how bad are these worms? At one point you were able to trick Pagurus into one of their traps and the result is pretty shocking! Just casually drags the giant crab under the sand whimpering.
• The Boss fights in this game have quite a lot.
  • Your first boss, Nephro... has dead crabs tied to posts. Approaching them after the fight doesn't reveal they're only captive—they're dead. And from Nephro's dialog before and during the fight, he fully believed he was carrying out the law. Not to mention he would have only gotten worse if Kril hadn't put him down.
  • The intro to the Duchess fight includes her gradually regaining her many crab legs instead of staying bipedal, crawling towards you while throwing up black liquid which is also on her face. When she looks back up towards the camera following her frightening speech, her eyes have gone from green with visible pupils to black, like all the other polluted crabs. On top of her unsettling demeanor and movements, there's her insane shouts and cackling throughout the fight.
    Duchess Magista: (In regards to her guards gone mad) Au clawntraire, little hermit. (Stands up only to fall forward and vomit a stream of Gunk) Our minds are clear as crystal now… (Jerks her tea strainer closer to her) […] I once thought my duchy quite beautiful, you know. Worth preserving. But compared to the reefs, it's a shameful, transient thing, destined to wash away. That's why I'm having them tear it down. (Magista's original crab legs emerge and touch down in the foreground from above as Kril watches aghast) I thought my beauty worth preserving too. (Rearing up while seen from behind) But of course my worthless life will wash away as easily as any other. (Looking forward to reveal her black eyes) Almost as easily as yours, little HERMIT!
  • One of the random boss fights you can encounter in the Shallows is the Royal Shellsplitter, who, if he grabs Kril, will slam him to the guillotine-like device while the screen goes black and you hear crushing noises. Even worse, sometimes Kril actively begs the lobster not to kill him as the animation is happening and it can cast a curse that terrifies you by screaming as it puts its head under its own guillotine blade and projecting a screaming face. You'll eventually encounter more of him as a Degraded Boss, but this appearance stands out in how easy it is to stumble across him before you have so much as even a shell on your back; He's literally a single right turn from out of the area where you first grab your fork!
  • Crossing the Sands Between always carries the risk of running into Pagurus the Ravenous. Unlike most of the bosses, the citizens of New Carcinia are very aware of him and desperately keep him at bay with repelling scents. If he grabs Kril, Pagurus will brutally grind him out of his shell with the butter knife tied to his claw and finish by eating the loosened hermit crab like an after-dinner mint. As a bonus, this is one of the few bosses that will harm other enemies.
    • This boss can be especially scary if you skip talking to the NPC's and wander around, where the music suddenly changes, a boss health bar appears, and this thing comes running after you from the dark blue very quickly.
    • Remember those Bobbit Worms mentioned above? Well, one of Pagurus' attacks has him move aside his eyepatch, letting one of the damn things pop out of the empty eyesocket to roar at you! Understandably, this will inflict the fear status effect on Kril just as easily as his roar, and much like Heikea, Pagurus will often immediately follow up with either his aggro attack or one of his two different crushing attacks, leaving you scrambling for either a replacement shell or the safety of the scent trails while the beastly crab chases after you with speed unfitting his size.
    • You may think that sticking to the beaten path is enough to keep Pagurus from devouring you, but once the time comes to search Flotsam Vale for the second map piece, you find out from one of Roland's trembling scrappers that the scent trails leading to the company town haven't been maintained, giving Pagurus free reign to pursue Kril until you can reach the relative safety of the settlements walls. And later still, you find out the final map piece lies within the stomach of the feral apex predator, meaning you MUST defeat Pagurus to proceed.
    • Honestly, Pagurus is a scuttling embodiment of nightmare fuel, right down to his appearance; His towering size is obviously intimidating enough on its own, but his sickly purple and pale green color scheme and the barnacles encrusting his shell give off the impression that he's more like a walking corpse than anything.
  • The Diseased Lichenthrope is... well, it's really hard to tell what exactly it once was. But by the time you find it, it's a creature covered in the Gunk and lichens, with its only visible features being its large mouth with tons of teeth, its tail, and the water can on its head. It will regularly launch crabs at you that are covered in the Gunk, too.
  • The Consortium is a cage full to the brim with crabs and lobsters along with at least one octopus, but that doesn't take away from its terror with its sheer size, the glowing purple eyes all over, and the fact one of its tentacles wields a flare gun that it will shoot at you. Furthermore, it can't actually be damaged by conventional means; you need to attack the knots of fishing net holding the cage together to deplete its health. And consider that you find The Consortium buried in Gunk, yet all the sea creatures inside swim away the instant the cage is broken open while leaving behind a great number of Umami crystals. Were you fighting them or the cage itself controlling them as an embodiment of the Gunk brought to life with Umami?
  • Voltai, the Accumulator is encountered in the power center of Roland's factory. Think about how electricity is a recent discovery for the ocean dwellers. He likely had Voltai locked in that singular chamber their whole life, and it's had a visible effect on them. There's a door Voltai could easily open with their electricity, but they seem to prefer their prison instead of trying to escape. Even worse is the implication that Roland has either thrown people in there or not cared when they fall in, with Voltai mentioning former "playmates" and how Kril is the first one to "stay awake" so long. This child-like Living Battery hasn't completely lost their mind to the Gunk yet—Roland did that before the epidemic got that far.
    Voltai: The world these days is dark and mean… Even the water tastes unclean. And even those you love and trust… Would rip your limbs off if they must! Like Mister R, the one in charge… Who scrapped our homes to build his barge! But don't be gloomy, glum or sad! Cuz down in here, it's not so bad! Save crying for another day! Forget it all! (Bursts from one of the garbage piles) Come on! Let's play!
  • Roland himself is a more realistic source of nightmare fuel..... At least, at first. His monopoly over the scrapping industry and the assistance of his assistant Inkerton is enough for him to keep an ironclaw grip over New Carcinia, but his boundless greed later drives him to scrap his own production facility so that his barge can make the trip to The Mouth Of The Drain, leaving his loyal workers stranded in a hostile environment surrounded by gunked crabs, certain death drops, and a toxic sea. Then he audibly relishes ordering Inkerton to kill the city folk, claiming that the only reason he didn't do so earlier was because he didn't have a valid excuse, before taking on Kril by using his cane (An Allen Key) as a bludgeon. Once you whittle him down to half health, he takes out five more and starts swinging with reckless abandon, gleefully ranting about how this fight is what "animals" like he and Kril were born to do.
    Roland: Yes....... YES! THIS IS WHAT WE WERE MADE FOR! ANIMALS, YOU AND I!
    • To add on to this, Roland has a chance to say shit when falling over. Yes. Not one of the words used in place of a swear, like "dear cod", and it the ONLY place in the game that does this.
  • After a sustained period of creeping around The Unfathom and dealing with the Demonic Spiders within, you'll probably be happy to finally come across a Moon Snail shell; Finally, you can warp back to New Carcinia to mentally recuperate and prepare for the trials ahead...... PSYCHE! In a move so cruel even Fromsoftware swore they'd never do it, Kril is spat out of the shell by a boss disguised as a checkpoint, Petroch, the False Moon, a much larger and tougher variant of the above-mentioned hermit crab enemies whose attacks cover the ground with hazardous Umami-infused crystals.
  • Inkerton in his youth was said to be a rather friendly cephalopod, but once his parents died in a scrapping accident and Roland took him in, he had no problem with "disappearing" the very same bottom feeders who used to be his neighbors. First, he'll ambush you on your way to Flotsam Vale, only sparing Kril once the fight proves to be more trouble than it's worth, then you fight him again in The Unfathom once he loses himself to The Gunk and suddenly blasts Roland's head open before turning his attention to Kril, bludgeoning him with his shell cracker and even crushing him inside it as a human would for his grab attack. All the while alternating between snarled insults and gleeful proclaimations about how he and Kril will die there together.
    Inkerton: Let's face hell together, lad!
    Inkerton: TO THE LAST, I GRAPPLE WITH YE!
    • Fridge Brilliance and Horror comes in play here: The last line before Inkerton's second fight starts changes to the front those affected by the Gunk uses, where his other text doesn't, suggesting he has entirely been fighting it this whole time and his anger towards Kril made him succumb, that it's why his behaviour changed so suddenly... or he's always been like this and the Gunk just brought it out. And all theories aren't pretty.
  • Camtscha, the Bleached King who let his paranoia consume him and kill the Hermit Elders that made the Perfect Whorl, so he could take it for himself. Unable to use its power, he hid it and ruled on regardless, even as the pollution drove the Old Ocean to ruin. And his continued fear of being ousted is prevalent in the dentures spread throughout the kingdom and especially his throne room as "anti-hermit crab measures." By the time Kril meets the king himself, the ancient crab is far from intimidating, unable to move his body and only attacking with his limbs and a toilet brush wielded as a scepter. After he's defeated, you receive the "Pollution Scoured" message only for a rumbling to shake the hall with a painfully loud cracking noise. Camtscha molts and crawls out of his shell, casting aside the coral crown and roaring as Camtscha, Reborn. If his fleshy appearance wasn't bad enough, his ranting comes out as raspy gurgles and hisses translated by the subtitles.
    "Damned sorcerer… We sentence thee to death…"
    • To suppliment his offensive against Kril, Camtscha Reborn starts off his second phase by grabbing a discarded pair of dentures from the ground and stuffing them into his mouth. They fit so well that they look disturbingly natural for a creature that has no right having visible teeth, and his bright red hide, raw and fleshy from his molting, doesn't help. And of course, getting grabbed by him at low HP results in the mad monarch putting his artificial jaws to use and devouring Kril.
• The Unfathom as a level is molded by every fear the ocean embodies; darkness, depth, and hungry creepy-crawlies. It's so dark you can barely see a few feet in front of you, barring the dull glow provided by the occasional glow stick or bioluminescent coral, so it's easy to get lost; even the map is shrouded by darkness. You can't leave until you find and defeat Petroch, and the predators down here are tailor made for ending the lives of poor little hermits scuttling blindly through the murk....
  • The tiny sand mites are almost harmless individually, but you'll never encounter them individually. They scuttle from small corners in groups of five or even more and ravenously cling Kril to drain his hp until he can shake them off. They're the first enemy you encounter at the bottom of the drain once Kril has abandoned all hope of retaking his shell, and if it wasn't for the timely intervention of Nemma, the poor lad would have been torn to bits.
  • Viperfish fight similarly to the hooked minnows native to the previous areas you've traversed, but compared to the minnows who mostly just blindly rammed you with the sharp object stuck to their heads, the Viperfish snap at you as ravenously as the dog enemies they were likely inspired by, occasionally roaring to terrify you.
  • As if the hermit crabs acting as "shell mimics" weren't enough [and don't worry, you'll encounter them down here as well], The Unfathom is home to an enemy closer to the more classic role of a mimic; one disguised as an item. Of course, it's an Anglerfish that uses its lure to imitate the shine of an item while it waits underground, and they can snatch Kril up in their hand-like fins and toss him into their massive mouths to devour him whole.
  • Appearance-wise, the Cuttlefish are a respite from the rest of the pelagic horrors and look downright adorable in comparison, but you'll almost certainly be unpleasantly surprised when they unexpectedly cast semi-homing Umami projectiles at you, being the first enemy in the game besides Grovekeeper Topoda to leverage the power of Umami against you. Later variations of them are also the only enemy in the game to utilize the hypnotism status effect; leaving Kril helplessly walking towards them while they either pelt him with their magic or crush him in their tentacles if he gets close enough.
  • The Spider Crabs. Dear COD, the Spider Crabs. Anyone who mistakes these goliaths for gentle giants due to their real life nature as harmless scavengers will quickly be disabused of the notion when they turn towards Kril and start charging up their eye beams, mouth agape and body glowing. Getting up close will get you no breathing room either, thanks to their razor sharp claws. And if they grab Kril, he'll be lifted level with their heads before getting incinerated by a sustained stream of their lasers at point blank. There is no kill like overkill, indeed!
    • Past the Luminous Respite moon shell, you'll be greeted by about five Spider Crabs patrolling the plateau. The solitary ones prior could be whittled down by taking advantage of their poor turning radius, but here you'll be lucky to pick off one without the others cottoning on and stalking after you from all angles while blasting you to pieces. The smokescreen shell spell is practically a necessity here. And there's a stainless relic right in the middle where they can all easily notice you. Good Luck.