This is a Horror Show adventure seed designed for Horror Show but intended for use with any system. The basic idea is to draw in characters from one or more existing modern campaigns for a one-shot horror show session. These can be from any genre or game system.
STRANGER THAN FICTION
Style/Budget: B Movie
Genre: Psychological Horror/Splatter-Gore
Location: An old asylum or hospital
Universal Law: The Power of Suggestion
Threat: Dr. Woodlock
The Characters in one or more of your modern campaigns receive invitations from Doctor Peter Woodlock to attend a meeting at Lynch Memorial Hospital, room 92 of the Sullivan Building. The message lists off their various accomplishments, all in quotes, and tells them that the very fate of the universe may depend upon their skills. The doctor is a mad man testing out a new therapy and treatment to help patients overcome post traumatic stress disorder. Before the players arrive, he laces the grounds with a gas of an experimental drug that makes people more prone to suggestion. Everything he tells the party is a lie designed to see how far he can push them from their accepted reality. He has made extensive preparations as well, creating fake footage, books, etc as needed. In the light of day such evidence is obviously fake, but under the influence of the drug, they are quite convincing. He hopes to watch as they descend into madness and violence, killing themselves or one another as he conjures monsters and vicious traps through the power of suggestion.
Lynch Memorial Hospital has been abandoned for fifty years. Anyone who investigates the matter before hand can learn this. When and if they arrive, the Doctor informs them that their lives are a lie, that they are not even real people. He explains that they are in fact characters from television shows, books and movies. What is more he has proof in the form of DVDs, books and movie posters. He even shows them clips of actors who play them giving interviews. If they still don't believe him, he points to all their achievements as evidence (whether they merely be heroic or are beyond human comprehension). If someone is a superhero, he points out that super powers don't exist in the real world. If someone is a vampire, he explains that undeath is a biological impossibility. If someone is an ace counter-terrorist agent or super cop, he argues that only in movies does law enforcement routinely save the world or stop threat in the nick of time. Whatever genre conventions or excesses your campaigns indulge in, Doctor Woodlock uses to persuade the PCs they are not real.
He says he realizes it is a lot to accept but assures them the situation is as he describes. He also says there is a problem. Something has gone wrong and in the last few days, they became real. And for whatever reason, it is all centered here at the Lynch Memorial Hospital. He explains that the hospital was abandoned and torn down ages ago, but that it appeared suddenly the day the PCs were brought into reality. They also detected strange energy readings coming from deep below the hospital. There is concern that they are at the epicenter of a fundamental breakdown of reality.
Much of what he says is untrue. The hospital was never torn down, but Doctor Woodlock expects they will buy his reasoning. The bit about the energy is also false. In fact, if he is pressed on what kind of energy exactly, he may falter before finally settling on Electromagnetic Radiation. Reality is fine, whatever world the characters have inhabited up to this point exists (and the Doctor is a part of that) but he is trying to present a more mundane world to them).
He tells them that strange things have been happening on the grounds of the hospital. That creatures from myth and legend have been appearing in the woods and that a vast network of caverns and caves stretches beneath the basement. He says that he believes this has opened a door into a reality that resembles the hells of so many different religions. He thinks somewhere on the grounds is the secret to what is going on with the PCs and he wants their help getting to the bottom of it.
In truth the doctor is merely interested in observing the party. His drug is effective but so much so that people affected by it will often harm themselves as they encounter phantasms created by the doctor's suggestions. As the evening wears on he encourages their delusions seeing how far he can push them before they kill themselves or each other.
To make this work, you ought to create real threats based on the doctor's suggestions. So monsters in the woods, traps and supernatural creatures in the basement and its caverns. You can also add in more suggestions from the doctor and elaborate as needed. The idea is to create a real meat grinder for the party that stems entirely from their minds. You can occasionally throw them hints that these are their own projections but be subtle. For instance you can give one player a slightly different, possibly contradictory, description of the same monster. The drug is effective and the players shouldn't discern any problems with their senses until the next day when the drug wears off.
Throughout the hospital there ought to be clues that can penetrate the effect of the drug, things the players can find that suggest the doctor was lying. Again you want to be subtle here if possible. And hopefully they question enough of their reality that even when presented with evidence against the doctor's story, they are not sure what to believe.
The Power of Suggestion: This rule means the GM can present any supernatural, scientific or magical phenomenon as if it is real, but then later hand wave it as illusion created by the power of suggestion. For example after being warned that werewolves stalk the surrounding forests, the GM could throw proper werewolf encounters at them, effectively treating them as real, with characters suffering actual wounds, even though these are all a product of the players' minds.