NetHack/Nightmare Fuel

"What could possibly be scary about a game made of numbers and letters?", you're probably thinking. Good question! Why not take a gander for yourself at the surprising frights NetHack has to offer?

Setting

 * The idea that you can eat any sapient or sentient being you kill as long as they're not the same species as you is... harrowing to contemplate at length.
 * There are lots of "used armor" shops scattered throughout the dungeons. Sometimes these shops contain cursed armor, which can't be removed, except by uncursing it or if the original owner dies wearing it. Now where do you think they got their inventory from?
 * Dying while in a shop confirms it outright - the shopkeeper takes all your possessions in that event (which amounts to making them part of the shop's inventory). Seems reasonable enough... but if you directly steal from the shop (e.g. teleporting out with unpaid items, digging out...), the shop owner will try their damnedest to chase you down. If you should die after that point, guess who comes for all of your loot?

Monsters
"Oh no, she's using the touch of death! Do you want your possessions identified? (y/n)"
 * Master liches and arch-liches are Demonic Spider (if not Boss in Mook Clothing) levels of frightening to encounter in normal gameplay, and it's even worse when a monster's polymorphed into one (which can happen with shapeshifters and polymorph traps that can spawn below dungeon level 7). Imagine you finally make it to DL 10 after a long and arduous series of splats, and as you're exploring something invisible warps towards you and starts destroying your armor, cursing your inventory - or worse, the infamous Touch of Death. Even if it isn't as likely as other outcomes, the fact that something can potentially teleport to you and render you a corpse with no warning will leave you double-checking every move you make.


 * Chameleons - in real life they're bizarre and unusual animals, but generally no threat to the average person. In NetHack? They're Hollywood Chameleons that can randomly turn into one of several eligible forms every few turns or so - including several more powerful forms that would be completely out-of-depth for a player otherwise! If you're especially unlucky, you might just encounter one in the form of the aforementioned master/arch-lich above...
 * The trolls found within the dungeon are incredibly strong and persistent for midgame foes - not only do they frequently generate with polearms that can swat you if you try to put another monster between you and them, but they have a nasty melee-range bite! To make matters worse, they have Regenerating Health abilities that put werecreatures to shame. Even if you manage to put them down, their corpse will revive as soon as possible, restoring it to full health and likely leaving any adventurer that struggled to defeat it just once at its mercy. If you're not prepared for them, your best option is to pull out the wands and spells, or else just run.
 * Even disposing of the corpse isn't always guaranteed to get rid of it - it's incredibly heavy, meaning you'll have to lug a lockable container over if you want to stuff them in, and spending turns carrying one heavy object to the other just increases the risk of it coming back to life. Eating the corpse seems most intuitive, but also carries the risk of it resurrecting with each turn spent, right down to the very last bite! (Strangely, carnivorous pets don't seem to have the same issue.) It's entirely possible to satiate yourself from low nutrition trying to finish eating a single troll! Out of the other "permanent kill" methods - stoning, disintegration, drowning, tinning, etc. - most of them might not be an option unless you have specific items, so you'd better hope the Random Number God is smiling on you.

Other characters

 * You. Yes, you, the corpse-eating, gold-stealing, magic-abusing One-@ Army! With the blessings of your god, you'll be wreaking havoc upon the dungeon and its denizens. Sure, most of them are trying to kill you first, but what of the ones who aren't - did that peaceful dwarf deserve to be robbed and killed just because you really wanted to borrow their pick-axe? Is it worth kicking every  you come across? Even without leaning heavily on moral angles, the sheer amount of killing and eating (usually involving the things you just killed) that you have to do would be thoroughly off-putting in any other context.

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