I've never actually run this scenario, but this is how it plays out in my head. Inspiration is derived from a fusion of the movies Eyes Wide Shut and Cube, as well as some of the more Cthulu-like moments from the classic G3 Module "Hall of the Fire Giant King."
As the party is passing through town, halfling thief stops to see some of her beggar friends-she helped them out back in the day, and they've helped her out a few times as well, being eyes and ears on the streets. She hears that some of her friends have gone missing. In fact, a number of people hae been mysteriously disappearing. Young and old, poor and even in one or two odd cases wealthy.
Halfling does some recon and detective work (attending wealthy parties using her hat of disguise), and finally puts together some clues that lead to a supposedly respectable noble family and their manor-it seems a lot of people go there for parties, but when she in disguise tried to attend, she was rebuffed. That and some other types of people have been seen by the beggars, but they've been too scared to say anything until they spoke to the halfling, who they know they can trust. These other people have been going to the house as well...and some of the nobles, when they get tipsy, have made some strange suggestions.
Halfling gets the rest of her friends, and they prepare to sneak onto the manor grounds to investigate...ready for any kind of trouble, just in case. Haflling briefly contemplated trying to infiltrate her way into the party herself, but then she realized that the nobles might get wise to that, as they're very selective about who comes to these things. Besides, halfling needs to be ready for trouble.
Sneaking into the manor, the halfling is shocked at what she finds-the nobles are involved in a twisted, hedonistic cult similar to Eyes Wide Shut with a lot of the freaky, Cthulu-like eddying lights, colors, and twisted wall scenery that Gygax first wrote about in the Temple of the Elder Elemental God in module G3. Look at EGG's descriptions there, and you'll get a good image of what it is.
The debauchery by itself is somewhat sickening, but it would be harmless.
That is...
...until the halfling sees what the nobles do to the people they kidnap. Suffice it to say that it doesn't bear describing.
And then comes the Cube inspiration. The kidnap victims are dumped into a dungeon maze riddled with traps and monsters that stalk the hapless prisoners, who are usually unable to fight back in any way. The hedonistic nobles watch the prisoners run around like rats in a maze, with nowhere to run and nowhere to hide, especially given the demons they've summoned to make the hunt all the more "fun." The prisoners are left to die like rats in a maze, while the nobles watch. Some of the prisoners are poor, given the aristocratic contempt for their weakness, others are nobles (not involved with the cult) that had previously insulted, snubbed, or otherwise offended the hedonists.
The halfling and her friends now have a choice to make-attack the hedonists, or try to rescue the prisoners, and risk letting the villains escape?
Well, it's not much of a choice, really.
The party ends up in a hellacious running fight through the maze, rescuing prisoners, avoiding traps, and fighting the monsters the nobles have rounded up, even as they deal with the cultists of Vecna, who in some aspects is a god of secret hedonism and decadence, who minister to the sick freaks that run the whole shebang. They confront the cultists, and capture some of them as the cultists try to escape.
The testimony from the victims, noble and poor alike, along with the evidence of the adventurers, is going to be enough to get the cultists impaled.
The intent here would be not so much to creep the players out, but to shock and horrify them.
I admit, I'm not so much a horror fan. To me, a lot of these monsters are bullies-but let's see how they fare against people who can actually fight back!
What if the ghosts of The Ring suddenly ended up with an angry Ghost Rider on their hands?
What if Michael Meyers suddenly realized he was dealing with Batman?
What if Leatherface and his clan suddenly realized they were dealing with an enraged Rambo, and the hunters had become the hunted?
I personally think you could make an awesome horror film where the roles are reversed-the Freddy Krueger/Jason Voorhees character is stalked, hunted and chased by something he can't fight back against, before he's driven crazy.
Not so tough now, are you?
