The skeleton of the adventure is the module "Beneath the Dust," which is actually a Dark Sun adventure. I call it a skeleton because I've modified it so heavily it's almost not the same thing, but the core element is: the quest for a Seed of Life (with which to ressurrect the dead valley).
A long while ago, someone here (I don't remember who) mentioned an idea that stuck with me and that I'd like to try now. The idea was that over the course of the quest, each character died until there was one left -- who had to give his/her life to complete the quest. Because this is a mini-campaign and we have no intention of returning to these characters, I think this is a viable idea and I'd like to try it. It certainly would bring a much different flavour.
However, because I know my players and what they like and don't like, the idea I have is this:
I'll run the adventure as normal. I think there are four or five encounters (not all combat; some are skill challenges or the like). At the end, when they've found the Tree of Life from which they can harvest the seed that will save their clan, they will encounter the Seed's guardian: a silver dragon. This dragon will issue them a challenge -- succeed, and he will hand over the seed with his blessing. Fail, and they all die. The challenge is where I was thinking I would bring in the 'last one standing' idea.
What I would like is a couple of challenges that requires one person to voluntarily stay behind for the good of the quest. I've got an idea for the first one and the last, but I need two more.
The first idea is the standard "one person stays behind to fend off hordes of enemies while the others escape." This is the first time someone will have to stay behind, and I intend for it to be the NPC (I know one character is very much the 'defender' type, so I'm half-expecting him to fulfill this role, which I will be prepared for).
The last one I intend to be a simple puzzle -- there is a large empty room whose door slams shut behind the last two adventurers. A large pressure plate stands in the middle of the room. When nobody is on the pressure plate, a portal back home opens on the wall (both characters free to abandon the quest and go home). When someone is on the pressure plate, that portal closes and another opens -- to the Tree of Life. In order to get to the Tree of Life, someone has to stand on the pressure plate and be left behind. I might make the pressure plate trigger something horrible, too, to ensure a sacrifice, like be in a pillar of flame or something.
Anyway, I find myself a little stuck, and I thought I'd ask if anyone had any ideas.
Because I like to tailor things to the characters, here's a list:
Asha, cleric of Melora. Older, calm, steady. (Player A)
Bear, warden. Stoic, military-minded. (This is the one I half expect to sacrifice himself first) (Player B)
Moss, druid, very insect-oriented rather than beast-oriented. Young, joyous, twin sister to Badger. (Player A)
Badger, rogue ("brutal scoundrel" build). Angry, rash, headstrong. (Player B)
Shadow, ranger, archer. NPC.
Badger and Moss are twins, and very young; barely out of adolescence. Because twins are so rare among elves, these two have a sort of "chosen ones" thing going on, and I expect (though do not require) that they will be the last.
At the very end of the challenge, I plan to reveal that all characters are fine. Yes, I am actually going to pull a "it was all a dream" thing on them, but I think it works in this case.
I should also mention one other thing: I only have two players, and they each play two characters apiece (with the NPC rounding out the party), so I'm not concerned about the player of the first character to die being bored and feeling left out. I hope I can encourange things to pan out so that the NPC dies first, then the character of one, then the other, and they'd both have a character at the final puzzle.
So! What I need are two more interesting challenges or puzzles that preferably a) require a voluntary sacrifice for the good of the quest, and b) are aimed towards a cleric and a warden or ranger.