
TitaniumStar |
So I am GMing a game in two weeks and my PCs feel that things have been a cakewalk. One of them requested that I shake things up by doing a more spooky, scary session. He wants me to "Freak Out" the other players and I thought this would be a good idea.
I've never ran anything to be particularly "scary" (but I am also a new GM). I was thinking of getting some inspiration from Silent Hill, and the Hills Have Eyes.
I imagine them finding an old, burnt down home, but further investigation reveals a trapdoor that leads to a basement which is still in tact. The room will be strange, with symbols and writing on the walls. Jars of pickled creatures. Maybe some chalk drawings on the floor. With a Perception check, they find a secret door that leads to an underground dungeon. After a series of traps (one which will separate the PCs from the two NPCs traveling with them), quick scares, and exploring, the dungeon opens into an enormous cavern that has a few hills with shabby looking houses on them. During exploring I will have monsters appear like half melted people, the bottom half of humans walking towards them (I was thinking the top half is there, just invisible and they can attack with claws), shadows, a being that is wrapped in stitched up flesh and all you can see is an eye looking at you from the opening (it wiggles around in the wrappings but can't walk, it instead teleports around and attacks with supernatural abilities), deformed humans, screaming skeletons, and maybe some zombies (Why not?)
The few homes will be wrecks. One will be a single room just covered in blood. Another may have a haunt.
The last room, as you walk up, you hear screaming. At this point (if the PCs didn't leave already), I will have a scenematic moment where this humanoid with a black bag over his head and a fake smile glued where his mouth should be, is standing in the middle of a room brutally murdering the NPCs. It should be clear that they get the /fudge/ out of there! The humanoid begins to move towards the PCs and a chase scene starts as they go back through the traps and hallways.
I haven't decided what happens to those who get left behind.
That's all I got so far. Please give your thoughts on it. I am willing to tweak it, or try something else new. My PCs are only level 3. lol My players have been getting a lot of treasure so I don't know if I want there to be treasure, or have it be purely for a story to tell.

TitaniumStar |
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I forgot to mention, that I was thinking of having these deformed and monstrous humans be tormented children of worshipers of Gyronna. This could have possibly been a site where a small community of worshipers was held.
Does that make sense? I'm not really sure of anything when it comes to religion in pathfinder. -_-"

Nargemn |

This is all in my opinion and experience, so take it with a grain of salt. I'm sure others will disagree.
Something unfortunate about Pathfinder when it comes to trying to make something 'creepy' or 'scary' is that Pathfinder is inherently a tactical combat simulator (when you get down to the core of the rules). This, in addition to the fact your players expect to be able to 'beat' whatever challenge you put before them, means that it will never exactly be 'terrifying'. Your content or subject matter could certainly be horrifying, creepy, and just downright scary on it's own, but it's unlikely to actually instill in them a true sense of terror.
The reason for this is your players are heroes - they can fight the villains and win. What really makes terror is facing down something you cannot deal with and have no real way to stop. Of course you can include things that make the outcome grim, such as their success hinges on some sort of sacrifice, or they accidentally unleash some monstrosity on innocents, etc. Ultimately, however, they'll expect to be able to beat what they fight, and if they can't, they'll probably feel cheated.
For a system that really does horror well, I really recommend Call of Cthulhu.

TitaniumStar |
@chbgraphicarts - The Tomb of Horrors seems like it would be a great dungeon to run, but at a higher level. xD I don't think my players have enough potions to last them the first room! "Falling stones inflict 10d6 damage"! Woof!
@Nargemn - Yeah, I agree. The rules do make it tough, but I feel like with good storytelling, there is a possibility I could send a shiver down their spines. lol
I am worried that they will turn around and try to attack the "Boss" and all get killed. I may need to use my powers of GM persuasion to convince them otherwise...which I try to avoid. But meh...what can you do for players who think they can beat anything. Just let them learn from their mistakes I guess.
I heard that Call of Cthulhu was fun. I will have to check it out. :)

Rynjin |

@John Kretzer - Haha! My PCs would poo themselves if they all got separated. Maybe if that happened, I could have less enemies and more traps and puzzles. The only thing I worry about with that is healing. I don't remember exactly, but I think there is only one healer in the 5 person group.
You're trying to scare them, remember?
Stop worrying about whether or not they can survive. =)
If you want to separate them, use some Haunts.
There's some that're pretty good at making PCs go off alone, or trapping them there if they do.
A simple Slamming Portal can work if you make it really jam a door shut once it's closed. First PC in is separated.
The Mourning Maiden can effectively trap a PC if one fails teh Will save.
Likewise a variant of Father Charlatan which traps a PC inside their own mind. Fluff it differently, perhaps it makes them think they're best friends with a child ghost or something.

Tormsskull |

So, assuming that all of your players are okay with being scared (some people aren't,) here are some suggestions.
First, indicate in an out-of-game way that the players have gotten themselves into an area that you didn't expect them to find so early. Maybe they fall down a shaft or otherwise get into an area that they cannot easily leave.
You have to be sincere about it enough so that your players think you're serious. Maybe come out and say that some of the enemies will easily kill the whole party.
Second, spend some time writing up some particularly chilling descriptions of rooms and enemies. It may sound corny, but if you can get a spooky soundtrack to play at a low level while you're gaming, it will help to set the mood.
Thirdly, make sure that the players never know when combat is going to break out. Have numerous potential threats end up not being threats at all. When the combats really do start, the players will not always be prepared.
Lastly, describe, describe, describe. While describing things, punctuate your descriptions with short pauses to let them sink in.
Good luck.

Jack of Dust |

Just make sure to have a Benny Hill chase scene. No horror story is complete without it!
Seriously though, if I were you I would pass notes to players. Exactly what they say is up to you. It could be something as simple as "You swear you get the feeling something is watching you". Also how much do these players trust each other? Leaving incriminating evidence that makes the PCs believe their friends may be responsible for murders goes a long way to up the scaryness. My GM did this when we did a horror session. I was playing a dhampir and when the party woke up, a dead body was in the center of the room with bite marks on its neck. This was just after the GM passed me an innocuous note. None of the party wanted anything to do with me because we were also taking wisdom damage every now and then due to "the whispers in our head". They believed I was going crazy.
Seperate the group but make it their choice. Make it so that the group don't trust each other. One of their party members actually turning against them, whether due to possession or mind control, can be very unnerving.
Finally, make sure to have some ambient music on hand and possibly make the room you're playing in dark with just one lamp at the table for sake of reading character sheets.

thorin001 |
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To scare the players you must tailor the adventure to play to the players' sensibilities rather than catering to the characters'. Mood music and lighting help with getting to the players. Also if you can involve things that you know creep the players out that will help out a lot. If someone in the group is bothered by cannibalism then incorporate that. If someone is bothered by enclosed spaces then put some of those in and take a lot of time to describe how tight and confining those spaces are.
I do not recommend splitting the party much. The problem is that you have most of the people sitting around just watching someone else. This is when the cell phones come out breaking immersion.

HWalsh |
1 person marked this as a favorite. |
I love doing this to players once in a while...
Here are a few tricks:
1. Torm's right, accidentally let it slip that they are in a place that you weren't ready for them to be in yet. Something like, just murmur, "I had hoped you'd come back to this around level 5... Crap... Oh well..."
Then press on.
2. This one is mean, but I had a GM do it to me once, and it was an instant classic. So I recommend this.
This only works if the players are in a house without small children running around. Set a heavy book on a high shelf that you have access to, take a piece of string, loop it around the book edge, keep the string near you (make sure it isn't a trip hazard) and use super fine string if you can so your players don't see it...
Then, as you are doing a description, include the line, "Suddenly, from somewhere nearby, you hear a loud slam!" reach below the chair and pull the string. A suitably large book will fall (preferably onto a hard surface or a box) with a loud slamming sound. Guaranteed to make someone jump out of their skin.
Warning: Doing this can very well result in someone spilling a drink, so time it cautiously... Also be prepared to dodge snack food projectile retaliation.
3. Props, props, and more props.
You can have all kinds of fun with props I once, for a horror prop, gave the players a small box that they found in the dungeon. It contained a spider (no not a real spider!) on a wire. When they opened the box the wire made the spider jump at them (Make a reflex save to avoid the spider and his bite!).
Again, be prepared for things to get thrown at you.
Then the mother of all props...
This one was a little pricey... There is a substance called Gallium it is a metal that melts at room temperature... You do have to be careful with it (it also will dissolve in water) anyway... I got a huge chunk of it (for like $50) and I made a hollow sphere, inside of which I placed a skull (bought it at a yard sale for $2) and as the center piece of the table that week, I placed the orb on a small pedestal (with a box lined with plastic around the base) and I ran the game as normal...
The Gallium started melting (at the top first where the light was shining down on it) slowly, the players didn't notice it at first, then they noticed that the orb was deforming as I was reading the main description of the place they were entering.
(I had practiced before hand so I had the timing about right)
as the gallium flowed down the pedestal the skull was revealed... It was pretty good at setting the tone.
(And since the Gallium was retrievable I have been able to use it for all kinds of things. Especially when teaching as the kids love tricks with Gallium.)

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In the old days I ran an eberron game and had my players enter the Mournlands. I kept looking online for ideas and found a forum thread named "1001 things to mkae sure your players never reenter the Mournlands". Most of it seemed straight out of silent hills but still. I used some tensed music in the background, reduced the lighting in the room one step and had them encounter those ideas.I went and planned several lines of description to spook them. I also overrided the ability of their character, the summoner couldn't get his eidolon or smaller summons while he was stuck in the flaming train haunt since it was all in his head. Now if you do that make sure it's a non-combat encounter, don't be unfair and tell them to fight in a way they wouldn't normally do(or do it, it would add ALOT of tension). 1 hour later they were already trying to run away as far as they could from the place. They still throw stuff at me if I mention the session.

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I am worried that they will turn around and try to attack the "Boss" and all get killed. I may need to use my powers of GM persuasion to convince them otherwise...which I try to avoid. But meh...what can you do for players who think they can beat anything. Just let them learn from their mistakes I guess.
There was an optional rule in 3.5 Complete Warrior which let you make a check to ballpark their BAB vs yours. Let them do that, or just a Knowledge check to know that they stand no chance in a straight up brawl.
But really - long-running campaigns & creepiness don't mix. This is because in a campaign - you don't want to have your characters have a good chance of death in any given fight. Much of what makes something freaky is that something might pop out and kill you any second.
Pathfinder does the former well - not the latter.

Joe Homes Editor |

A few recommendations:
1. Lose the map, especially if your group is used to playing with one. I don't agree that Pathfinder is bad for horror, but I know that map-based tactics are, because they give the players too much information. Everything is psychologically less scary when the players can see the whole room at once, and know where enemies might be hiding—there are no "shadowy corners" on a map. This will also force you to describe things more.
2. I would not recommend splitting the party, as it will break immersion, but I really like the idea of pretending that they're somewhere that you didn't expect them to be. However, only do it if you're typically a well-prepared GM; my players would see right through this, because they know I never plan my games that far in advance.
3. Don't count on scaring PCs away to start a chase scene. If the paladin sees one of his friends being murdered, he will go bring justice, and now you have a combat on your hands. Rather, a ticking clock mechanic (combined with the big bad) is much more effective. Set the house on fire, or have a portal to the Abyss slowly devour it, or something. Something that the PCs don't have the tools to fight that says "if you stay here, you will DEFINITELY die." That's not to say that having the NPCs murdered won't be effective and spooky, especially if the PCs are fond of the victims. Just don't expect your typical adventurer to turn and run at that point.
4. BE CAREFUL with your players' actual fears!!! It's fine making someone a bit uncomfortable to tickle their fear response, but it is very easy to go too far and make someone genuinely uncomfortable. Beyond being inconsiderate at best and dangerous at worst, it's also bad for the game.
I always go by the quote from Declan Donnelan: “The space must be safe so the performance may be dangerous.” Players will shut down emotionally if you make them too uncomfortable. It sounds counterintuitive, but if they feel personally unsafe, they will stop being scared, and might even get angry. Either way, they won't be having fun. It's best to make a safe atmosphere (though feel free to play up the ambience with music and whatnot) so that your players remain engaged and emotionally open (and thus easier to scare). The whole performance revolves around their trust of you, so maintain that at all costs.

cnetarian |
Don't use a trap door, have the floor collapse under their combined weight and send them all into a basement room with walls covered in runes that they really do not want to touch, as would be required to climb out. At this point you should mention that you hadn't expected them to come here before they had access to a fly spell, but that there is another way out and you're pretty sure that they might be able to handle this dungeon with their NPC's firepower, so you'll just roll with it as is.

Rynjin |

This all kind of depends on one thing: How scare-able are your players?
IME it's hard to cultivate a real atmosphere of fear since, well, everyone knows it's fake. At best you can creep them out somewhat, like a horror movie. If any of our players are horror junkies, you're fighting an uphill battle already. It already is, since people in groups don't get scared nearly as easily.
That's part of why people are suggesting stuff like "split the party", because then you can A.) More easily make their characters afraid (and get some RP out of that, which leads to people getting more in the mood) and B.) The players feeling, at the least, a fear for their characters' safety (because again, people in groups are harder to scare, and a group of PCs especially given a PC party can take on pretty much anything).

Dave Justus |

While running a regular boring pathfinder game, have a friend who is not in the group turn off the main breakers in your house, make thumping noises and then jump out wearing a hockey mask and holding a butcher cleaver.
You did say it was the players you wanted to scare right?
Alternately, pain is scary.

SmiloDan RPG Superstar 2012 Top 32 |

Give them costly choices. Negative levels, loss of valued magic items, crippling injuries, loss of prestige, loss of allied NPCs, horrible curses.
Like, the PC has to choose to use his magic sword to keep a portcullis open or have it slam down and watch an NPC get butchered.
Or make the choice between saving another PC or losing the McGuffin to the BBEG. With dire consequences. Like he uses McGuffin to burn down their favorite inn or the temple they get healed at.
But you have to be careful and not ruin their fun or mess with their characters so much that they're no longer fun to play.

Bloodrealm |

Give them costly choices. Negative levels, loss of valued magic items, crippling injuries, loss of prestige, loss of allied NPCs, horrible curses.
Like, the PC has to choose to use his magic sword to keep a portcullis open or have it slam down and watch an NPC get butchered.
Or make the choice between saving another PC or losing the McGuffin to the BBEG. With dire consequences. Like he uses McGuffin to burn down their favorite inn or the temple they get healed at.
But you have to be careful and not ruin their fun or mess with their characters so much that they're no longer fun to play.
Those suggestions aren't scary at all - just cruel. I don't even know why you brought those up in a thread about trying to run something scary.

SmiloDan RPG Superstar 2012 Top 32 |

Yeah, it's a fine line between scary and cruel. And I definitely don't want to be cruel to the players. But sometimes it's fun to be cruel to the characters--if the players agree.
I know I've had trouble making something scary in PF because a lot of things that would normally be scary: ghosts, serial killers, zombies, rabid dogs, spiders, elder evils, redneck zombies, mermen, etc., because if it has stats, the PCs can kill it. And something that is hard to kill isn't really scary, it's just frustrating.
I think some of the scariest things you can do in RPGs is to force the PCs to make hard decisions with dire consequences. It can be cruel, and that is regrettable, and it's also why I don't try to be scary too often.

Third Mind |

From what I've experienced, the best thing for inflicting fear is the unknown. The monsters get a lot less scary when you finally see them. So, I'd suggest emphasizing descriptions and how a situation COULD be potentially life threatening or worse for their character.
"As you proceed down the corridor, the musty smell grows as the darkness intensifies. Finally, you reach the end. A wall with numerous deep, hand sized holes stands before you. Dried blood streaks trickle down the edge of each of the holes, and as you look down, you just see a pool of more barely dried blood. Painted in a familiar crimson above the holes reads, 'Pick one'."
Not very scary, but that was off the top of my head and onto the computer. The idea though is that they don't know what will happen if they thrust their arm into the wall. Will it get bitten? Straight up chopped off? Will it turn into a tentacle? Does putting their arm into the wall even mean they can continue on? Or is there another way out?
If you want to do creatures, look for ones that can stay hidden. Shape shifters, extremely good stealth users, even a good illusion user could mean making the party turn on themselves, or on a town, etc...

Turin the Mad |

Take something that they perceive to be all cute fluffy bunnies of happiness ... and make it into a horrid tentacle monster with unfathomably horrible nastiness. Halflings summoning Dark Young of Shub-Niggurath to devour their own families. Bunny smites. Attic whisperers. MLP: FiM going full "Overfiend".
Atmosphere: fog, semi-discernable sounds, unintelligible gibberish, faint smells of less-pleasant 'things', dim lighting (in-game).
One trick that I rarely use, but to good effect, is a seemingly "Q" type wishcrafter of phenomenal cosmic power that wants silly things, like fresh fish, scented flowers, or whose fur feels as soft as a bunnies that, as it turns out, transmits rot grubs. Not the nice kind of wishcrafting, either.
"I wish to be beautiful forever." *pouf* They're now a gorgeous nigh-indestructible crystalline salt shaker, the soul of the recipient bound within. They still feel every grain of salt that pours through their head/face, trapped in a silent scream, arms clasping their heads in eternal agony.

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Actually - if you want to freak out the party - possibly the best way is with the cooperation of one of the other players.
Not good for a long campaign - but fun for a one-shot, or even a 2-3 session campaign.
Make the top villain an unknown. The party fights minions etc, but the villain himself is always at least one step ahead of the party, always knowing what they'll do before they do it. Prisoners die before they can be interrogated properly due to 'suicide'. The villain is... one of the party members!
He can try to split up the party - get other party members alone to deal with them 1v1 - maybe with a couple monster buddies.
It's fun because even if they get clues which points to a party member - their meta-knowledge knows it's not him - so they dismiss it as a frame job. I did this trick once in a whodunnit style 2 session thing. I made it so that the clues were really obvious if that one player didn't do anything - but he planted a few misleading clues and everyone assumed the real clues were just him being framed.
In the end he led the group into a crypt (he was a necromancer) - they actually helped him raise a bunch of undead so that they could 'set a trap' there for the real killer - and he murdered them all. :P End Campaign.

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One thing that worked for me last time I had a need for that was throwing them into the underdark... naked... and not the "civilized" underdark with the drow cities and such... the part with strange aberrations and slimes.. and in my case... Daemon infested.
When I said to my players to wipe clean their inventory I received a few "I'm going to keep it for when we find our stuff back"
My response was that their stuff was hundreds of miles away and probably already got sold. Find a sharp rock or the leg of a table from some ruins.. that is your new equipment.
That did shake things quite a bit, especially since there was no full caster in the party so they all kinda relied on their equipment, and the encounters were not balanced for their situation either, some were doable, others were not, and it was on them to scout ahead and find a path that did not lead to something monstrous and with damage reduction that they had no chance to challenge in a fight.
That lasted for several sessions, nobody died in the process and once they came out they quickly found enough gold to return on par with their level expected wealth.

Turin the Mad |

A4 (1e module) does exactly what Scarletrose says, albeit it's a one or two session deal. You're stripped nekkid and have to figure out how to escape the verminoid monsters, a cave fisher ... tough going for a lot of characters that don't think about losing all their stuff.
The ceiling monster is a "lurker above". The floor version was, IIRC, a "trapper".

BadBird |

Here's one possible idea for a little psychological terror:
Part 1) The party discovers a crude pictogram in a conspicuous place that appears to be drawn in blood. It represents a figure with a calm expression but a menacing posture holding up a knife or a spear in a manner that suggests stabbing. Studying it seems to cause fleeting daydreams of being harmed. There is an easily uttered phrase of several syllables, apparently gibberish, scrawled below it.
If a player utters the phrase aloud in the presence of the pictogram, everyone around becomes disoriented. Force will saves against nausea that persists until a save is made or the character moves away.
Attempting to discover any magic behind this image reveals absolutely nothing magical.
Part 2) Another pictogram with the same text below it. This one depicts a figure, smiling, and with open arms, being deliberately stabbed in the heart (blood everywhere in the picture) by another grinning 'friend'.
Now start throwing will saves at players at random. On a failed save, the character begins to unconsciously mutter the gibberish phrase to themselves - quietly at first, but growing in volume. When another character calls the muttering character's attention to this behavior it stops, but the character in question has no recollection of it and is momentarily disoriented.
Attempting to discover any magic behind either the pictograms or the bizarre behavior now causes pain and disorientation, and still reveals nothing.
A sense of a stalking presence begins to grow among the characters. While fighting a battle momentarily puts the odd behavior on hold (and can be used to snap the party out of it), the characters discover that they're feeling excited and a little giddy about violence.
Part 3) More pictograms, one by one, as the party progresses. One image may detail what seems to be a 'casual' decapitation between apparently consenting figures with only random lines where faces should be. Another may show a circle of figures with faces that have only circle-eyes, where some are spearing others, or being speared, or both.
The party begins struggling a little to control the muttering behavior. Then, upon failing a save one of the characters also - and again, without any consciousness of the act - draws a weapon, or if already holding a weapon begins making idle little chopping or stabbing motions with it. As before, intervening ends the behavior with side-effects, but characters must succeed at a will save to put the weapon away.
In addition to previous problems, investigation into the phenomenon now brings on strong attacks of the behavior.
The presence is now felt as a force of will, like a pressure behind the eyes that will very reasonably go away if the character would just accept it a little...
Part 4) Where to go with it depends. It can simply be background 'noise' as the party goes about clearing the place, or the behavior can escalate into calm, methodical acts of violence - a character failing a save and casually stabbing another, or suddenly grasping for another character's hair with a knife in hand. You can play it deus ex machina, where the appearance of enemies, or the enemy, stops the situation from getting out of hand with everyone failing saves and starting to end up like the pictograms...

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What level are the PCs?
A large part of book 2 of the Rise of the Runelords adventure path is a haunted house. And I do mean that literally - I think there are something like 14 haunts overall, plus more tangible undead for them to fight. I think it's intended for around level 4 or so.
There are great suggestions in the RotR sub-forums for how to enhance that atmosphere when running that section of the adventure. It's not really lethal, but it is really, really creepy. If you're going for horror in Pathfinder, this is a good place to start.

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I ran a haunted tower scenario where I gave all the players cards from a deck that I had made up. Occasionally I would draw randoms card from the deck and exchange them with the players.
Most of the cards simply said "keep calm and carry on", but some of them had special notes like "Your character is sure that the ranger is trying to kill him" or "you hear faint music coming from the west" or "begin repeating the following nursery rhyme over and over until someone asks you to stop. Your character doesn't know why he's doing it" or something like that.
Honestly though, the things that PCs find creepiest are things that fall outside the normal game experience: goblins that gibber dire warnings at you but won't fight. Weird noises that come from nowhere. Corridors that lead to spaces that can't possibly exist. Objects that disappear and reappear without warning. Evidence of something dangerous that must be nearby but which nobody can find. Terrifying creatures who are themselves scared and blubbering in fear of something worse.
Finally: trap them someplace that they cannot rest and start plinking away at their hit points VERY SLOWLY with small environmental and encounter hazards. It will be annoying at first but as they slowly burn though available healing resources they'll start to realize that they are the frog in the stewpot and the water's getting slowly warmer.

Joe Homes Editor |

...The things that PCs find creepiest are things that fall outside the normal game experience: goblins that gibber dire warnings at you but won't fight. Weird noises that come from nowhere. Corridors that lead to spaces that can't possibly exist. Objects that disappear and reappear without warning. Evidence of something dangerous that must be nearby but which nobody can find. Terrifying creatures who are themselves scared and blubbering in fear of something worse...
Exactly! This is why I advised that you ditch the map. If the world is drawn out in front of your players, they feel rooted and in control. If the world is violating the rules they thought they knew, they're engaged and FREAKING THE EFF OUT.
Finally: trap them someplace that they cannot rest and start plinking away at their hit points VERY SLOWLY with small environmental and encounter hazards. It will be annoying at first but as they slowly burn though available healing resources they'll start to realize that they are the frog in the stewpot and the water's getting slowly warmer.
This is great advice! But see if you can find a subtle way to get rid of those pesky "wands of cure light plot tension" before sending the PCs in there. My players rarely care about serious damage taken during a fight, because they know they can retreat and whack each other with a wand until they all feel better. Once they're down to 10 or so charges, things start getting interesting. Maybe a monster or haunt that depletes wand charges?

My Self |
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People aren't scared most by what they see, but rather by what they imagine. A creaky, stale-smelling mansion with faint trails of some strange, unidentifiable liquid and glimpses of a silent fleeting figure is far more frightening than saying that they're in a haunted house and see a CR 1/2 goblin running around.
Also, players get scared witless when you make them roll will saves and whisper or pass messages for only single players to see. And they'll be on their toes if they make a perception check, but you say that "everything appears normal", even if in fact that is the truth.
The scariest thing isn't something frightening, it's the absence of something expected.

My Self |
Also consider covering over parts of your map so players can't see it all. Ask "are you sure?" frequently. Be descriptive, but show, don't tell. ("a tall, earthy green, squinty-eyed person" vs. "an orc")
Enemies who seem to violate laws of reality make for frightening combats. The Terminator was frightening in his first appearance because he simply didn't die. A sort of enemy who gets up repeatedly after being "slain", and simply doesn't seem to stop no matter how much HP damage you deal to it, would likely be scary for your party.
Oh yeah, and Call of Cthulhu is scary because you guys are the weak ones.

M1k31 |
I would over-populate the map with character "echoes"... NPC's that are there with those that are not, both helper and foe, then have both interact with each other... while some are 100% unable to harm/kill anything, the others are, allow players perception checks to tell the difference(tell them on prepared paper notes... if you want to make things really difficult number everything, keep a notebook with the real/not real list for separate encounters, allow each number to be real or not depending on the encounter... and allow players who fail the perception DC to acquire the wrong impression the exact same way), but give them Will saves required per minute(if they fail they must wait 1 minute before they can try again) to tell the others what their character see's.
Alter terrain erratically as though spontaneous entangle spells were activating and disappearing, swarms, wisps, echoes, maybe throw a vigilante or 2 in(so they can be the party's friend as social and an over-leveled big bad as vigilante... maybe even make them some kind of cult that cuts and runs when the party is winning and then dies to the horrors of the haunted/cursed location...) make a bunch of the traps non-lethal(just increase the amount of them to the ridiculous), pop up CLW potions in hidden niches as needed to allow for true horrors and dangers...
Make it difficult for the party to actually kill/overcome a foe and get the experience, yet also able to escape most actual "death" scenarios(imagine the parties surprise if a PC dies and you pass them a note telling them "you have not actually died, your character was sitting in a chair in the room next door, when the party reaches you, you know nothing about the doppelganger that just died under a massive zombie swarm they are running from... or anything from point A where this character was separated from the party, act ignorant of the horrors they encountered and annoyed that they made you wait for them so long").
Edit: on that last note... if you allow enough of the party to die and regenerate that way, you can also give some PC's added notes like "you now want to kill (other player) without the party knowing" and "You receive flashbacks of your deaths", or "you know who killed you", allowing the players themselves to add to the horror as the party turns on each other and becomes afraid of the other players as much as the dungeon itself even if they lose some sense of danger of death.

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Also, players get scared witless when you make them roll will saves and whisper or pass messages for only single players to see. And they'll be on their toes if they make a perception check, but you say that "everything appears normal", even if in fact that is the truth.
This was pretty much my point in recommending part 2 of Rise of the Runelords. There's a house with tons of haunts, and some of the GMs who have run it have shared resources here on the forums.
When I ran it, I had my players roll 40 or 50 d20s and right down their results for me, so we wouldn't slow things down as we went. Every time someone triggered a haunt, I'd use that for their init and will. And I'd sit there handing out slips of paper to individual players, so they could "see" stuff that the other players didn't. With 14 rooms of that crap, on top of normal undead encounters and stuff that they could all see, it was some creepy fun and really freaked them out. Especially since a couple of the haunts force PCs to attach each other!

BlackJack Weasel |

do you ever take people outside and have private conversations with players during the game so you can give them information that you don't want the other players to know.
cause if you do that you can always say, make a player fall into a pit of spikes after failing a reflex save. then take that player outside and tell him, they didn't really die but not to tell everyone else. so they think that they might of actually just died. little things like that. really test there saves.