All right, since there seems to be good interest, I'm going ahead with this. I'm going to start the plot two days from now, on Sunday 14th my time, and will probably close it off next Saturday with another post. These are the details I've worked out, which I'll be linking in the start-off post on Sunday.
THE CAUSE
The post on Sunday will feature a statue/stone thing out in some obscure area of the woods that your characters will be lured into finding. Looking at this statue is going to induce the crazy, but it's not going to be one look = full blown insanity. There will be three levels of it, basically, depending on how many times you look at the statute. Each night in camp, characters who looked at it the first time will feel compelled to go back and look again. Either they do, or they don't, depending on if their will is strong/they get sidetracked/their friends noticed they're insane and tied them to a bed.
ONE LOOK: Twitchy paranoia. Kind of like how people act in horror movies when there's no music and they're heading towards a door which is obviously a bad idea. Jumping at shadows, that sort of thing.
TWO LOOKS: More paranoia, coupled with a tendency to snap at people and assume the wrong things. For example! "Nice day, isn't it?" "WHY WOULD YOU SAY THAT TO ME? WHAT ARE YOU TRYING TO PROVE?!" "...that it's... nice out?" "...oh." They're not completely nuts, but they're definitely hearing and seeing things that are not quite what they should be.
THREE LOOKS: Jack Torrance land. Everyone's out to get me, I can't trust anyone, if they're going to come after me I should kill them first, CAN YOU HEAR THE SCREAMING OF THE LAMBS CLARICE, etc. The important thing about this level is that it is AXE CRAZY. They will try to hurt people! If you don't want to play your character at fullblown knife-murderer level, then just don't have them look a third time. How you play it is up to you, but the concept of this plot is that characters become unhinged and do dangerous things.
Those are the general effects of the statue! You can play these out however you see fit, those are just guidelines for how severely your characters are affected. I've done it like this so there's wiggle-room, and so you can flip your characters up a notch whenever you can during the week. I should mention though that it will take at least three days for them to hit level 3, since the statue will only be crazy-inducing once a night. Otherwise it'd be too easy to find and destroy.
"But Klavier, I don't want to play my character as a complete psycho for four days while I wait for the end of the plot :("
THIS IS WHERE OPTION TWO IS. At the end of the week, I'll be doing the second post, where the unaffected characters can find the statue and destroy it. Since that would be a really boring boss fight (how hard is it to fight a piece of rock), there is the added hazard of immediate insanity during this post. Basically, if your character looks at it the wrong way during this post? Insta-snap, and they'll be at level three until the statue is destroyed. That way, you'll have other people to contend with until someone lands the lucky blow. This will be especially useful for characters who would be hard/terrifying/REALLY DANGEROUS to play as insane for more than a few minutes (but you still really want to be because damn that's cool).
And there's the rough idea of it. Questions, comments, "jesus Klavier that's too much to read, shut up" can go here.