On the fluffy front: Description! Description! Description! Not everyone is a wordsmith. I still use the dungeon dressings table from the DMG 1ed. I want a massive list of evocative scene ideas that really get under the players' skins, something that really twists the serrated edge of that hooked knife under the kneecap. I want the dining room description that makes the players twitch. Something along the lines of a pit trap filled with a swarm of infants' arms, covered with pustules of maggotty, rotting flesh, that try to strangle trap victims. I'm not looking for a gore factor, more of a little fluff item that really sets it in the players' minds that this BBEG is evil, VILE evil. I want the candelabra on the dining room table to be made from the still-twitching fingers of the last group of heroes to break in. I want the dinner served to contain worm eggs that will hatch inside the PC's stomach. At first, the worms are helpful - giving bonuses vs. poison & disease, but then they mature, and they become hungry for something a little more rarified but non-lethal. Like fingers and toes. Imagine the PC waking up one morning and discovering that his little finger is gone, with only a ragged hole remaining (no blood, no gore, no hp loss - the worms are your friends), and seeing a worm stick its head out, wiggle a bit like a real finger, then crawl back inside...
I want that description to tie into the plot - where the BBEG has possessed the princess's body, and he's about to jump into that summoning circle with Demogorgon: Thus fulfilling both ends of his contract - an innocent sacrifice, and giving his soul to the Demon Prince - only to be reborn later in the plot as something truly vile. Maybe even back in his own body, where the princess's spirit is now trapped. Thus creating one heck of a moral dilemma for our heroes - kill the BBEG to stop the sacrifice, and they slaughter an innocent - an affront that their gods cannot ignore. Allow the BBEG to make the sacrifice (with the goal of rescuing the princess later), and they doom her to a spiritual intimacy with pure vileness that will drive her insanely wicked (and a willing participant in his plot to sink the entire kingdom into the lowest, foulest, soul-devouring pit of the Abyss). The clock is ticking...
I want vile temptations, items that allow a PC to convert so many hit points of damage per hit into non-lethal damage -- at the cost of a little piece of his or her soul. The advantage: Every bit of healing the PC gets heals both the regular and non-lethal damage at the same time. The disadvantage: Every use of it makes the PC a little more... tainted.
I want to see some support for a taint system - either a new one or one that's already published. Something along the lines of the aforementioned vile temptation item: Each use of it (unbenknownst to the player/PC) racks up a point of taint. After 15 points, the next time the PC is low on hit points, he hears a whispery voice: "I can cure you, but you must do something for me in return. There is a man, an evil man, a murderer. You must slay him before he kills again." In reality, the evil man reneged on a deal with the demon the temptation item is linked to. Thus, the PC willingly becomes a servant of vile evil by carrying out the demons revenge... and sinking further into corruption himself.
This sort of work is very specialized. I can do some of it for myself. What I need are more IDEAS.
P.S. Please put an index in any sourcebooks you write! They make this poor DM's life so much easier!