Few forms of RP are as fun and rewarding as a possible excellently run horror game. You may be taking your players through a zombie-ridden post-apocalyptic wasteland or plumbing the depths of an Gothic nightmare, pursuing atmospheric chills and creeping out your players is as worthy an effort as it can be hard to achieve. Nothing will electrify your players as a truly terrifying session, and absolutely nothing is more memorable than scaring their pants off. However, running this sort of game can be incredibly challenging: what do you need to do in order to succeed?
First, you need to distinguish between two fundamentally basic forms of play. When it comes to a horror game, you can opt to either target terror or horror. Aren't seeing the difference? It's simple: terror 's what occurs when you achieve an elevated state of psychological fear, while horror originates from revulsion and disgust. Wading by way of a room that's hip deep in moving areas of the body would elicit horror: it's gross, it's unnatural, it's brimming with blood and flesh and intensely physical. Being haunted night after night by a mystery spirit would elicit terror: the fear is that of the unknown.
There is absolutely no right or wrong when it comes to choosing your thing, and you can switch with shod and non-shod if you are careful of methods you do it. Just remember that this basis of horror arises from realizing that we are mortal, that our bodies are just bags of flesh and blood that could be torn apart, which there are monsters in this world that would delight in doing exactly that. Think of movies such as Hostel or Saw; these 'torture porn' movies are about how each character will die, and how gruesomely, not about whether will all survive.
The cornerstone of a terror game comes from mankind's oldest fear, that's fear of the unknown. Farmville is infinitely harder to run than a horror game, because the DM you must make an effort to build up the terror with mind games, descriptions and atmosphere, instead of by simply throwing blood at your players. The goal is with the player's imagination against them, to give them enough gruesome clues to allow them to conjure up the worst possible scenario, and then reel them along with a sense of inevitability to the terrifying climax.
Whilst you should pick a basic style to check out overall, there is no reason you cannot switch from one to the other occasionally to further your needs. A long, drawn out game of psychological terror can descend into horror in the final scene as everything becomes physical, just like a game of physical horror can be produced all the more terrifying by inserting long moments of dread and suspense. Everything you can't do is mix them up randomly; finely time consuming moments of terror will be undone by shambling corpses, just like hour's worth of hack and zombie slash can make it very difficult to transition in a moment of fine tuned terror. So pick your overall mood, and then use each scene and scenario to help that very theme. Being clear sighted concerning your objective will help you immeasurably in presented!