I've only outright scared them once. I've made them nervous for their charaters, but I've only ever SCARED them once. I use music extensively in my games, and so that added to his, but I really think the delivery is what did it.
It was kind of a cutaway scene, for one character at a time (two characters in this game, just me and two people). They go to sleep, and they each dreamt. After doing one (which creeped her out, but wasn't even close to my finest moment), I did the other.
Dreams are definitely a good way to go, and the key is how you do it -- I think a lot of gamers are sarcastic to a fault, and one quip can ruin a scene if it's done at a bad time. When I read all this off the sheet to him, I kept my voice calm and conversational, but very steady and constant, not letting anything devolve into comedy. When the emotional part happened, I hit everything rapid-fire, not letting them do anything but process what was being said.
Background: I run a Final Fantasy homebrew and the character in question, Kogel, left his island at five years old after shooting some marauding soldiers in freaky-accurate-child fashion, and only remembers seeing the island village in flames as he sailed away on a boat the next day.
This is the write-up of it from my notes, hidden because it's kind of long. The general feel of it still carries over well to text.
[sblock](cue calm island music)
The sun is rising, and the rays are shining through the trees in the same way that they always have. The air is a little salty, but no smell has ever been so comforting. You see Michael and Adrian, two of the local kids, running through the little street with a blitzball under Michael’s arm. They’re heading for the beach to practice. Adrian swears he’s going to be a big star once he grows up big. He might, you can never keep up with him.
Miss Jones is on the front porch of her small home, playing with Lamec, Adrian’s younger brother, on the porch. He turned five this past month, and is anxious to start running with the other boys to go play blitz, but he’s not big enough yet. Such a nice, chipper little boy.
Dolors runs after Michael and Adrian. They always teased you about her, since you and her are better friends than she and they are. Standard little kid teasing. The four of you are inseparable, though.
Glenn, Dolors’ older brother, walks behind them, and waves to Miss Jones and Lamec as he goes. He’s not out fishing with his father today, staying back to keep an eye on Dolors and the rest of the neighborhood kids. He’s always testing you, getting you to run faster, be stronger, act more like an adult. He’s always pushing you in a friendly way.
Your mother comes running out of the house, looking a little distraught. She’s got a bag over her shoulder, and looks right past you as she runs by. You hear Glenn ask her a question about you, when you’re going to be coming out to play. But you’re right there, aren’t you? She bites her lip, trying to hide forming tears, and she says that you’ve got some chores to take care of first before you can come out. Glenn asks if it’s anything he can help with. Your mother shakes her head, and then leaves.
You see her go down towards the beach. She must be going to see your father off on his fishing this morning. He must have overslept; he’s very strict about punctuality, but he oversleeps sometimes on these really nice mornings. The Fastiloficans don’t really get active until mid-morning anyway.
Michael tosses the blitzball back over his head to Glenn, who doesn’t expect it, and bumps it to the side. You try to catch the ball, but it bounces off your fingertips. It hits the ground, and the village is in flames.
(fast-paced chaotic music)
You see a body on the road, burnt beyond recognition. It twitches a little, and you hope that the person is dead, for their sake. Miss Jones’ house is on fire, and the porch where she and Lamec were playing collapses as you watch. The blitzball sits at your feet, smoke residue starting to hide its colors. In the distance, you hear screams and someone begging for her life. You’re worried that it’s your mother. You’re worried because you know it is.
You burst into your home, pushing past the flames that choke your breath an sting your eyes. You know just where to go in your home, following the hallway into the bedroom, where your mother is trying to fight off a soldier, just like those from before, burned into your mind. He looks at you -- there is no face on this soldier, just that blankness or hatred you feel inside you. You watch him shoot your mother, and then he walks right towards you -- right through it, his body passing through yours as if it's not even there. You chase him out of the house, but he's not there when you stumble out into the road.
Voice: “You’re here every night. You are destroyed each night, yet the next you return.”
There is a small child behind you, looking up at you calmly. You don’t recognize him at all. He’s wearing shorts and sandals, with a small hooded sweatshirt, blue in color, that partially hides his face. You can’t see his eyes, but you can feel them. Around you , the fire rages.
“But this is the first night you remember, isn’t it? It’s because it’s different. What is different?”
A loud, sharp bang momentarily deafens you, and your entire body goes cold and numb. You slump face first onto the ground, pain creeping up your body, starting in your neck, and you see blood spreading, and it has to be yours, and behind you, you hear someone speaking, his voice cracking with pain and emotion and tears, “Why? Why? Why did it happen? Why did this have to happen? Why did you have to kill everyone? Why did they all have to die? Why do I have to kill you to make it right? Why must there be this fighting? Why can’t this all be over... why can’t I have peace... why was it TAKEN from me... why...”
The little boy leans down in front of you, and says in that same conversational tone, “This is different. Good-bye, Karl.”
("Kogel" is an alias -- Karl is his real name, that he doesn't use since he left the island.)
[/sblock]
The other player slept fitfully that night and was wiped out the next night, and she knows she dreamt SOMETHING about that flaming village that kept her from sleeping well. Kogel's player, my roommate, wandered into his room after the session, sat down on his bed, and just passed out dead asleep for 12 hours, and spent the next day walking around like a zombie, mind blown, he said.
You have to know your players, and know that it works for them and won't be too much. I wouldn't do anything that involves rape because that would make all of us uncomfortable. Freaky dreams, though, are always great.