I wonder if it would work not to threaten the PCs themselves (or close NPCs like family, friends, lovers) - just show how everyone else will die or be transformed into some horrific creature in whatever is creating your horror scenario. And they must really feel that if they fail, things go bad on a big scale - like every single human in a 100 mile radius transformed into an undead, or having his head explode, or maybe just everyone being infested by a parasite that will control their brains...
Well, I am not sure it would work or is enough...
I suppose another part of horror is the fear of the unkown and the uncertainity. That a monster might be hidden behind the face of a perfectly normal person - that suddenly lashes out and tries to kill you - and then disappears again. That a monster might be behind every corner...
See my post above —
especially the part about fear (as an emotion) being an instinctive response to perceived threats or danger. It is entirely possible to elicit a fear response by threatening things that the
player cares about. That's the thing, though. While most characters ostensibly care about the welfare of the world, the relatives of their PCs, etc. . . I've found that few
players care about these things.
Eliciting a genuine fear response from a player
requires that the player be made to believe that things they value are threatened or placed in danger. Their PC is the obvious target for such danger, as it typically represents the largest emotional investment of the player in the context of a given game. In this instance, if a player feels that their character is truly in danger and the rules of a game support this reality, fear is an easy emotion to elicit. The less perceived danger, the less fear.
That said, the mere presence of danger will not elicit fear in the context of a game. As I briefly mentioned earlier, I've found that a perceived threat or danger only elicits a true fear response when it is directly related to a decision that the player has made. Completely random and indiscriminate danger/threat is the stuff of satire, not Horror (look at Paranoia for a great example of this in RPGs). The realization that one is responsible for their own fate, OTOH, is a truly terrifying moment, for many people.
You
can move past using a player's character as the primary conduit for generating an emotional response of fear, though doing so treads on ground that most gamers I've met are not ready to explore in the context of a roleplaying game and that most GMs I have met are too blunt to manipulate in the context of anything other than pure shock value (in fairness, though, I think that this same handicap also applies to many authors of horror fiction and horror film directors).
I think that this gets to the bottom of why many people consider Horror to be the hardest genre to master in the context of RPGs. Too many people focus on the visual trappings of the genre, while ignoring the emotional aspect entirely or fearing to indulge it (there's some irony) for fear of violating social taboos. As I mention above, all the werewolves and vampires in the world won't drive fear into the hearts of players if they lack any substance, when it comes to actual play.
Personally, I've only been truly
scared when playing
one RPG campaign in the past 18 years. It's worth noting that I play more Horror games than any other type of RPG. Prior to playing this one game, we (i.e., the players) wrote down very real, very specific, very personal fears, on index cards for the GM and collectively said "These things scare us without touching on anything that we consider to be off-limits!" (of course, some of us were willing to lay bare some pretty personal stuff in exchange for a good scare).
For those willing to take the plunge, creating a list of 'talking points' like this for the GM is a good, effective, tool for groups who
are willing to move past the comparatively superficial ploy of using the PC as the sole conduit for provoking emotional response from players. Addressing real, personal, fears of the players during the game shortens the distance between Point A and Point B on the road to a genuine fear response by removing another barrier to raw emotion (i.e., the artificial construct of the imaginary player character).
How far any one group goes with this is up to them, but at this point I warn that you're really moving past what most folks commonly consider a game to be and into the realm of psychodrama. I cannot stress enough that this is not, under
any circumstances, a path that I recommend to casual gamers, emotionally insecure sorts, or the like. Such play experiences should
not be pursued by people who have not considered (or do not understand) the full ramifications of tinkering around with the mental and emotional welfare of other human beings.
And you
can take things even further (though I'm inclined not to discuss such methods on a forum). As for that one game I mentioned earlier? More than a decade later, I still walk a little bit faster and look over my shoulder a little more often when I travel alone, on foot, at night.