The Horror
So it comes down to determining what really does make them freak out. At best, I can probably strive to make them uncomfortable, but the difference between taking players outside their comfort zone vs. making the game unpleasant to play is a fine line. This makes horror gaming an intensely personal experience, customized to each particular group. There's no simple guarantee that something's horrible: one player may find Y'golonac a disturbing manifestation of sexual fetishism while another may find a headless fat monster with mouths in its hands to be absolutely hilarious. All I can offer is what worked with my group, and what didn't.
But before we go into that, it helps to define what horror is in a gaming context. I don't know that I can do this topic justice, because horror genres have been dealt with many times before by those more knowledgeable than me (see Ken Hite’s Nightmares of Mine). Here's the genres that I find more relevant to an action horror campaign and my attempts that both succeeded and failed in evoking horror.
Shock
Surprising a character, and thus surprising his player, with a sudden event or action. Surprise is one of the easiest thrills a game master can go for. You can just scream in your players' faces if you want to shock them, although you may get punched in the face later. But there are subtler ways to shock your players with props.
Failure: Having played with my gaming group for over twenty years, they are practically mind readers. George and Jeremy, in particular, can spot plot twists a mile away. It's gotten to the point that I've had to second guess myself and do the opposite of what I would normally do, because these two players know me that well. This isn't even necessarily a problem unique to me; they can anticipate plots of published scenarios too. When an allosaurus exhibit featured in Dreams Dark and Deadly, Jeremy immediately pegged it as a monster that would later attempt to eat them. In fact, that's precisely what the scenario called for, so I skipped it.
Success: Guppy, while telling the other agents about a monster he saw outside in a snowstorm, didn't realize that the monster was looming just outside the window behind him. When I showed a picture of the scene, of a victim staring at the viewer with the monster in the background, it shocked the players. They let out a whoop and laughed hysterically about it, a sure sign that I surprised them in a good way.
Danger
The character is in immediate danger. It's hard to make a player feel concern for his character if he's used to seeing hit points or other measures of bodily harm. So the way to make this really scary is to threaten a different form of harm: damage to ability scores, insanity, or a fate worse than death.
Failure: The majority of the scenarios involve a final standoff against a Big Bad, be it a monster or a cult sorcerer. As a result, the players are often overmatched, forced instead to follow a particular weakness or plot device that will trigger the monster's downfall. There's no simple means of just "beating" the bad guy, and sometimes this aggravates the players. It also means that at times, they are less concerned about their characters and more about the numbers of the opponent.
Success: Hammer and Jim-Bean are ambushed by ghouls. The ghouls keep trying tactics to capture the characters rather than kill them, and with only two players in that session, the scenario took on a desperate struggle. It wouldn't have happened with a larger group or with opponents that simply wanted the characters dead. It was clear that something far worse than death would happen to them if both of the characters fell, and that freaked the players out.
Body Horror
Body horror is the worst kind of personal horror, exemplified by the movie Alien. It's about horror so personal that it's INSIDE you, the horror of disease and self-loathing. This is a personal horror, which like danger is difficult to pull off if a player doesn't feel connected to his character. If anything, body horror is even more personal than danger. The way to get around this is to make body horror happen to other characters and let the player make the leap about what it might mean to happen to them.
Failure: Archive, poisoned by a tcho-tcho dart, dreams of eating a crunchy meal. When he woke up from his delirium, blood dripped from his chin and his pinky was missing. Joe L, his player, wasn't impressed.
Success: A shapeshifting blob that can absorb human flesh lurked beneath Groversville. An entire platoon of agents was dispatched to contain it, and while the players had an interpersonal squabble in a church, the platoon disappeared. As Jim-Bean faced down the shapeshifting monstrosity, he noticed it was dotted by weird patches of hair. That's when Jim-Bean realized that it had gotten bigger, and suddenly he knew what happened to the platoom – they WERE the protomatter spawn. Jeremy was definitely disturbed by that revelation.
Weird
Incongruous circumstances or experiences that simply don't fit in with what the player knows about the universe. These bizarre events upend the scenario if not the character's worldview.Failure: An investigation of a UFO's database revealed that humanity was created as an accident by the Elder Things. None of the characters had a strongly realized worldview and thus reacted to the horror of their insignificant origins with a shrug. This is one of those modern difficulties with Cthulhu gaming. In the twenties, earth shattering revelations about the universe could feasibly evoke squeals of horror. In the modern world, where we think we know everything and nothing at the same time, discovering you evolved as an accident from an alien Petri dish is just one more crazy theory on the Internet.
Success: Hammer received a package sent from the past containing information from the future that was, by all accounts, sent by from a future version of Hammer. This was the first time I actually weirded out George, who found the concept both intriguing and disconcerting as he investigated himself.
The Unknown
Using the unknown as horror largely depends on what the players already know about the campaign. In fantasy and sci-fi campaigns, the unknown is more difficult to pull off – Cthulhu fits right in with the rest of the cast at the Cantina. But in a modern campaign it's a little easier because the players assume they already know "the rules" of the universe. This makes the unknown possible, the thing that they don't quite fully understand but feel they MUST understand to succeed.
Failure: Playing in a campaign with Cthulhu-esque elements means that reality can take a weird turn at any moment. It's very important to slowly introduce certain supernatural elements and provide some consistency, lest players become so unmoored from reality that they just assume anything goes. This was most apparent when the agents were stuck inside Daoloth, a scenario that riffed on the movie Cube. The twisting of time and space simply confused the players and they meekly went along for the ride rather than role-playing their characters as horrified by the bizarre events.
Success: During a scenario in which I relentlessly killed off supporting characters, throwing a serial killer, a creepy kid, a threatening telephone call, and a lot of misdirection at the agents, the thing that freaked out the players the most was a box.
A simple cardboard box. The box dripped blue goo. Something flopped wetly inside it.
This stupid box, which wasn't relevant to the immediate plot but rather a plot point for a future scenario, consumed the players' attention. They were convinced that it was an alien entity, a hungry monster, a virulent disease, a human head, the list goes on and on. I had planned all sorts of horrible events for the scenario, had every creepy trope I could think of, but the stupid box was what put them on edge. Why?
Because they were convinced that it was part of something bigger. A box, dripping blue goo, in the hands of an escaped convict who had dabbled in technologies man was not meant to know…it all just spelled danger. They hated the box. They feared the box.
I didn't plan this. But when I realized that the players were disturbed by the box's contents, I played up the mystery. The convict who owned the box refused to tell them what was in it, which made things worse. They were willing to torture him out of fear what was in the box. When they finally did open it, they locked it in a sealed fish tank. You'd think the box was a nuclear device, the way they reacted to it.
What was in the box? It doesn't matter. What matters is what each player THOUGHT HE KNEW what was in the box. And that was far better than anything I could come up with.
Lesson Learned: Horror arises organically from the group, so roll with it and seize the moment when you spot it.
