PF/3.5 Could use assistance brain-storming a horror session

[Chronikoce]

I am planning to do a Horror session in the ongoing campaign for my D&D group. We meet on Fridays and I can't pass up this chance to mess with them terribly.

They are currently on a damaged riverboat which they plan on taking down river and I figure the easiest segue is that the night is foggy and when the fog starts to burn off the next day they are somewhere else.

Anyway here are the basic ideas that I have so far and would love additional evil, terrifying, and mean ideas to use against my poor players.

Plot Ideas
Damaged river boat floating through fog. When the fog clears they are on an open ocean with only a small island visible in the distance. The island is forested (possibly jungle) and is inhabited by 100 or so people. They all act really weird (friendly but in the eyes darting about and laughing at nothing sort of way that makes people wildly suspicious).

These people are either possessed, cultists, or something. I want all of the adults to actually be more or less normal people that are terrified out of their minds. The real threat will be the children. They will act like normal kids who are scared and worried about why all the adults are acting so strangely. In reality the children are the evil ones who are tormenting the adults and using them in the rituals/sacrifices/other evil plot devices.

Ideally the children will manage to get party members alone at some point and that is when I will hand that player a handout explaining that they have been tortured, abused, mentally assaulted, and ultimately possessed. When they rejoin the party they will be working towards the goal of enslaving their fellow party members!

Any ideas on how else I can be totally evil to them?

I won't tell them that character death is fake (i.e. if they die their characters will wake up on the boat with some mental stat damage or something). I don't want a real TPK but if they all die in the session and think that their characters that have been in play for over a year IRL just bit it then I want that to worry them *Insert Evil Laugh*.

I am thinking about using some sort of madness effects, maybe from Heroes of Horror or something to mess with them. Any systems better than that one?

--Edit--
The party is currently level 7 and we are playing PF/3.5 mix

[Phelix-Mu]

Point 1: Make darn sure your players are okay with butchering children if your device is going to force them to do so. Some people will balk at this pretty hard.

Otherwise, that's a pretty good premise.

Thoughts:

- Have a smouldering "bonfire" in the middle of the village, from the night before the party arrived; all of the adults refuse to look at it or go near it. Close inspection reveals what just might have been human bones among the ashes. The children, of course, take every opportunity to squick out the adults over what was actually a classic witch burning (though it wasn't a witch, and everyone knows it).

- Have you ever looked at the Unholy Scion or Daelkyr Half-Breed templates? Those are pretty much the 24 karat of creepy children premises.

- If you really want to crank it up to 11, the children are actually all spontaneously arisen undead, after the adults participated in a series of child sacrifices to save their village. Unfortunately, while this sounds golden, it is actually very close to the plot of Storm of the Century, which was on tv, so there's a fair likelihood that someone might know the premise. Happily, if the children are actually angry spirits/slaymates/whatever, then the characters might not have to butcher them, just right the wrong that has them hanging around and tormenting the adults and send the kids on to the afterlife.

I might have some ideas later. I believe Daelkyr Half-Breed is in Magic of Eberron, and Unholy Scion is in Heroes of Horror (but could be wrong on that last one); they are worth reading given how well they match up with your premise.

[Chronikoce]

My group regularly does everything but what I expect so I imagine they will find some way to deal with this without butchering children.

I do have 1 player that would oppose killing children both in and out of game so if you have ideas on how to get creepy children aspect but where they aren't really children (or at least there is some way to save them) then I would appreciate it. The spontaneously risen undead thing sounds really excellent. Most of my players don't watch TV (Netflix, Movies, and Anime is their go to media).

Unholy Scion sounds excellently twisted but I may have to tweak it so that redemption is possible. The Paladin in the party would probably crack under the strain of having to slay children who cannot be redeemed.