“Enact a 'sanity' system. whenever the player loses sanity points, hand them a slip of paper with a phrase/command/nonsense on it to represent the voices in the their head.
Make it sound harmless at first:
"Stare suspiciously at the player to your left, then draw a finger across your throat. Deny everything afterward."
"You suddenly have a craving for steak. Rare as possible."
"Everything will be OK. This is not your fault."
As things progress, make them more and more malevolent and creepy:
"Until you cut it out, we will always be able to track you"
"It's weAring his skin. iT's watChing you frOm behind hiS eYes"
"Please wake up. None of this is real. You're just having a nightmare. Please wake up."”
“Give them a stat that doesn't really do anything. Whenever things get tense, have them roll it, then pretend to jot down some notes. Makes 'em paranoid as fuck.”
“The party moves their conversation into a room which they can lock and is private so they can discuss their plan. Suddenly a knock is heard on the door. If the party ignores the knocking, it will continue. If someone asks "Who's there?" There will be no answer. The knocking will only stop once a party member opens the door. The doorway will be empty and so will the accompanying hallway. The party member can then shut and re-lock the door. A short time later, the knocking will come at the door again. Once again, no answer, and when the door is opened,the knocking stops. Shutting the door again, the party member only has to walk away from the door for a moment, before this is another round of knocking. This time when the party member opens the door, there will be a piece of paper laying on the floor at the foot of the door. If the PC reads the paper, it will say:
"Now we are all inside."”
“You may have to use your DM powers to just plain old fuck with the players. I once had a mission that ran through a haunted mine. There were un-killable monsters, sections of tunnel that were never the same twice, I would change details and act as if I never did, I would be purposely ambiguous about my descriptions of things, and I would implement plenty of "false trails;" hinting that something is about to happen but it really doesn't. Another good thing is to just make your players roll for stuff when they're just walking along. You don't even have to tell them what, or they could be rolling for nothing, as long as they believe something bad might happen.”
“Have the PCs in an area with a wall sized mirror and a strong light source. As they're passing through the room, the light flickers. If the party looks at the mirror, they see their shadow instead of their reflection. If they look at their shadows, they instead see their reflections, which smiles calmly and mouths a phrase before the light flickers again and everything returns to normal. If any PCs can read lips, they would understand the message: "Now it's your turn to switch around.””
“A tumbleweed blows across the street. Funny; they're not native to this area. It blows back again the other way. The PCs pass it. It starts to follow them. It has teeth.”
“The barber pole lights up and starts twirling if a male PC passes it. Raw screams can be heard from inside the shop, though there's nobody to be seen. The screams sound as though they are being made through a gashed throat rather than someone's mouth.”
“If the PCs venture into the cinema, a perfectly ordinary movie is playing (something the PCs would be familiar with), but all the characters are dead.”
“The supermarket/grocery shop is offering a special on eyeballs.”
“The PC's stop at an abandoned diner; the name of a missing/deceased PC inexplicably appears on a long-discarded menu.
(Today's Special: John T. Smith
-John Smith Chops
-John Smith Stew
“Corpses lie in the streets, quite obviously dead (gangrenous, bloated, all that), surrounded by clouds of buzzing flies. Every so often, the corpses swat at the flies, but then lie still again.
“The PC's encounter another "traveler", a man/woman/child with no weapons and absolutely no flaws at all, physical or mental. The person is extremely nice and helpful, and the monsters seem to avoid him or her. Beneath the streetlights, it seems like you can see the person's shadow moving in strange ways out of the corner of your eyes. Its movements don't correlate to those of the person casting it.”
“An orchestra is apparently taking place within one of the buildings, which has flickering lights in the windows. It grows louder as one approaches, but as soon as you enter the building from which the sound emanates, the lights go out and there is the sound of hushed whispers. Investigation finds a conductor's music stand and seats for all the band members, but no one is there. Occasionally a whisper comes out of a darkened corner.”
“Hoarse whispers float up from open manholes. "Save me," they say, accompanied by the sound of grinding rock and splashing sewage.”
“The player walk past a graffiti-covered wall--one prominent piece is a child's drawing of a door. Behind them, they hear the sound of a very rusty hinge squeaking. If they look back, the door is now real, and open.”
“There it is again.
They didn’t imagine it the first time they heard it. Shuffling footsteps that are intermittently carried on the still air of this unnaturally quiet town. Also, the faint clink of what sounds like chains being dragged.“
“As they walk through the swirling white silence they think they hear a pit-pattering echo to their steps. The soft noise stops each time they hesitate, so that one cannot tell if what they heard was real or just a figment of their apprehension. They feel the cold chill as a drift of the fog caresses their faces. It is then that a soft child’s voice whispers, “Tagged, I’ve got you!”, then a giggle in a high sweet laugh that seems to come from every direction at once.“
“They hear the yowls of a distant cat fight, which is strange because they have yet to see any animal life since coming here.”
“When gazing into a reflection in a pane of glass, a PC sees briefly the face of a dead loved one looking over their shoulder.”
“Pieces of shredded newspaper blow down the street. If a character reads a piece, the text therein at first seems to be describing their personal failings, predicting their doom or revealing some deep personal shame, but on second glance this is just a coincidental sentence/headline to an otherwise unremarkable news story.”
“You and a friend sit in the living room watching a videotape you made of yourselves talking at around 4:30 AM a few nights ago, laughing at your nocturnal antics. As you enjoy the absurdity of your conversation, you notice that the figures on the screen have stopped speaking, and are staring intently. As this continues, you start to speak to your friend, when you're interrupted by your videotape counterpart saying exactly the words that were leaving your mouth in a mocking tone.”
“Billboards or posters advertising the PC's and their various sins and flaws.”
“Several monsters re-enact an important scene from a PC's life, with just enough details (a certain jacket, out of place props) for the PC to recognize the scene, even though all of the dialogue consists of grunts and growls. If the PC's allow the scene to play through to its completion, the monsters revert to normal behavior and attack.”
“A school bus full of child-like monsters, apparently asleep. They can wake up.”
I hope you (and your players) have found that the wait was well worth it.