Arravis said:
I'm thinking of running a one shot Call of Cthulhu game so I've been looking into ways I can put some fear into my players. I am not sure what plot I'm going to run yet though, I might have to re-read my old H.P. Lovecraft books

. Anyway, I'd love to hear stories and advice on the scariest games you've had for any system...
My advice would be to know your players. Come up with things that would unnerve them (though not too much, as you want them to in the end say they enjoyed it.)
Second, come up with situations that would scare YOU. Chances are, many of your fears will be your players' fears.
Some really off-the-wall ideas from a CoC game I ran early this year:
-Tub of running water. Most players will think to shut it off. The water's amorphous tendrils reach up to attack the PC. If it grabs them, it pulls them in, and the surface tension becomes rubbery and unbreakable. Bullets bounce off, knives slide as if on a teflon bubble, etc. The other PC's must watch their friend down in plain sight.
-Everybody's gotta go sometime, right? To the restroom, that is. In the restroom, the toilet, sink, showerstall, etc. are VERY cramped. Trouble is, it seems to be getting more cramped all the time. Eventually the PC realizes that the whole room is shrinking, yet the door frame is remaining the same. The door opens inward, so they cannot leave unless they are able to break the door down. The outside PC's can either help, or watch their friend eventually get squirted out the bottom of the door like toothpaste.
-Flying animated kitchen knives and skillets are always a treat.
I have others, but they were really more specific to the adventure I ran. To me, being in plain sight of a friend and being unable to help save them from death is a very nasty thing to see. Plus, if their spirits come back as revenants, they have something to be pissed about - especially if the friend ran away in the end because they couldn't stand the sight.