What's the Freakiest/Most Gruesome Things That You Have Put in your Campaign/World?

[Retreater]

In a city of tieflings they had a decadent bar with tables, chairs, mugs, plates, etc., made from carved people who were then petrified. The heroes, unsurprisingly, didn't want to dine there.
The people had donated their bodies (after death) to be used by craftspeople and artists to be immortalized in this city of bard colleges. It was gruesome, but not necessarily evil. (Inspired by a gruesome exhibit I saw in real life.)

 

[loverdrive]

She is the most beautiful woman you've ever seen. You want to hold her close, to feel the touch of her silky skin. You want to marry her, be one with her, and be happy, to never again experience dangers and worries of adventuring.

You feel like you're drowning in her deep blue eyes, each fourteen of them. You kiss her, you feel each of her razor-sharp shining tongues in your mouth, to feel your warm delicious all-so-human blood drip down your chin, feel your loving heart tenderly pulled out of your chest as a testament of eternal unity.

Passion and anticipation is throbbing in your mind, you're about to enter her most private parts, her temple of love, and you almost feel the holiest of fluids slowly dissolving your flesh, your bones, your soul.

 

[Bohandas]

I briefly drew a webcomic set in D&D's Abyss, it featured several things that would have been messed up if they weren't so cartoony (the spoiler below is due to the size of the images, not their graphicness), for example, the protagonist reads a magazine called "Hot Bodies" which features depictions of people being burned to death

Spoiler

EDIT:
There was also an unneeded discursion about the fact that those spiked tentacles are ovipositers, their desire to lay eggs in various characters' bodies, and the messed up circumstances of how those eggs came to be fertilized


EDIT:
Also, and admittedly this one's about a non-RPG game, but I've actually had custom cards printed up for Cards Against Humanity that are more outrageous and offensive than the official cards

 

[Voadam]

Sometimes it is the little things.

The PCs were in a crypt getting some supplies hidden there long ago by a death angel sect. There was a little ragged hole in a wall. I described some chittering, and a couple went up to the hole to listen better. I then said a long thing with lots of legs and clacking mandible pincers shoots out, I wiggled my fingers and shot my arm out across the table in a weaving sinuous line. Seeing some of the players shudder and recoil was particularly satisfying as others were shouting out "Kill it! Kill it!"

Best giant centipede I've used.

 

[Imaculata]

In my 3.5 pirate campaign, the sea of the dead spilled onto part of an island when a tribe of witches tried to open a gateway to the realm of the dead. Part of the island came alive; a ghastly mount of flesh, which then separated and became the infamous living Island of Damnaur.

 

[Alzrius]

I actually never got a chance to put him in, but I really wanted to put in the monster known as "the Man at the Bar," from The Book of Unremitting Horror (affiliate link) into one of my games.

In short, the MatB is a sort of native-outsider, an earthbound-demon, who preys on souls of the lonely and the desperate. But rather than devouring them in some back alley or killing them in their sleep, he frequents dive bars and zeroes in on people drinking alone. Pretending to be a kindred spirit in a "life's got me down, too" way, he plies them with alcohol, using magic to keep them depressed even as he puts a hand on their back, which is when he starts draining their soul a bit at a time (i.e. hitting them with negative levels), until their head hits the bar, looking to everyone else like they're dead-drunk, when in fact they're just dead.

Unfortunately, I couldn't ever figure out how to make it work; the best option always seemed like a murder-mystery, but I never had the chance to pull it off where it would have a more X-Files-like theme, rather than the usual "here's another monster to kill."

 

[Umbran]

So, what do you have? I'm excited to hear!

An entire planet covered in a thick layer of goo. The goo was an infectious biomass that had the tendency of splicing DNA between creatures so people infected, before being reduced to goo, would sprout and transform bit of various other creatures. So, like, a human would develop pincers from the microscopic mites on their skin, but giant sized, and so on.

And, of course, the transformed monsters on the surface had claws strong enough to pierce most biohazard suits. And while you are walking around, you only have a limited amount of air...

And, also on this planet, was a Geigeresque temple. Under the temple was a giant vault filled with fat-eating vampires, the only creatures immune to the goo...

 

[Blue]

I've described some horrid abominations, but sometimes it's the everyday, taken up a notch, that gets to you. The party was in the rough equivalent of the Underdark, and the cave they were following brings the out pretty high up in the wall of a cavern. Earlier they had been dealing with mutliple sets of purple-decayed creatures working together in eirie silent coordination like some sort of hive mind.

The have a ledge up here they can observe from and can make out giant albino-white worms or snakes down there among the giant fungi forest, as well as the underground river they were looking for and needed to follow downwards. The party works out they will build canoes from the stalks of some of the fungi, but need to beware of the white worms they might be hostile.

They have their plan, start down, and one throws a torch down not near where them to see if it will distract the worms.

At which point I describe as the almost-solid carpet of purple cockroaches spread in perfect coordination away from the flame, how they are a a living mass that covers everything to a depth of several inches - except the worms.

The worms were not hostile and in fact the only safe place to be. Tense issue with makign a fire barrier to hastily hollow out canoes with the purple hivemind swarms tried to engulf them.

One player told me next session he had nightmares. I dialed back on real bugs after that.

 

[Blue]

Oh, in a humorous vein, in a tundra the party came across a herd of dire sheep. The ranger made friends with the dire rams and it didn't look like there would be combat. Everyone was relaxing when I turned to the nearest player and quite loudly bleated like a sheep "BAAA!"

The player jumped up in their chair. We all had a good laugh.

 

[Blue]

An entire planet covered in a thick layer of goo. The goo was an infectious biomass that had the tendency of splicing DNA between creatures so people infected, before being reduced to goo, would sprout and transform bit of various other creatures. So, like, a human would develop pincers from the microscopic mites on their skin, but giant sized, and so on.

And, of course, the transformed monsters on the surface had claws strong enough to pierce most biohazard suits. And while you are walking around, you only have a limited amount of air...

And, also on this planet, was a Geigeresque temple. Under the temple was a giant vault filled with fat-eating vampires, the only creatures immune to the goo...

Pishtaco? Pishtaco - Wikipedia