When I first began The Abyss Project, I joked it would very quickly become "Evil Forest, Other Evil Forest, Yet One More Evil Forest", etc. This is pretty inevitable – there’s no way 666 layers, or whatever fraction I do before I give up, can avoid some forms of thematic repetition. There’s going to be a lot of desert layers, jungle layers, etc, and there’s inevitably tropes and concepts I come back to as I tear through my mind in search of what I find creepy/scary/gross/etc.
I really didn’t want to hit "Evil Desert" quite so soon, though, it’s just that the term "Cactus Demon" lodged itself in my brain and would not leave. I really wanted to create an "old west" sense to this layer, without necessarily putting demons in cowboy hats. So there’s a "frontier fort" with a greedy merchant who controls the water supply, and, well, cactus demons. I could go totally nuts here — I had thoughts of rampaging gnoll-spirits who hunt the Thirsty Dead, demon-buzzards, and so on… but the fact is, with 666 layers to fill, I try to keep myself to one idea/concept/gimmick per level. So there will be gnoll demons somewhere else, and probably a layer called "The Plain of Feasts" where the wicked are condemned to be eternally devoured, and so on. I’ve got names and brief ideas for the next 15 layers or so, at least, and they seem to come as fast as they’re consumed.
There’s a real temptation to do more stuff in-depth. I’d like to detail up an interesting ship for the Salt Sargasso, or do more about Dustblood, or create more eyes for the web (how about a beholder with no body, just eyes floating in a linked mass?), but I only have so many hours in a day, most of which go to my day job and my paid writing. (As of now, this website has earned me, oh, 2 bucks or so.)
Some other notes:
Zungol The Water-Trader: One of the biggest hurdles I had with the 4e mindset is the idea that NPCs can just be built declaratively, without needing a class and a level. This is odd, because that’s exactly how HERO and GURPS work, and they’re generally my favorite systems. 4e lacks any point balancing beyond setting upper and lower bounds for things, though, and that’s perhaps where my trouble lay. Anyway, Zungol is my first pass at an "NPC" built straight from the monster rules, with whatever stuff I felt someone of his level and position ought to have. He started with an area-effect burst that did damage and prevented anyone struck from targetting him unless they saved or Zungol attacked them, but I decided that might be too powerful and frustrate players too much for 4e, which really opposes anything that can limit player actions for long. (And I’ve seen people fail 4 saves against being dazed in a row…) Exactly what Zungol is, I am leaving up in the air for now. He’s a skinny spiny blue guy who sells water. Everything else is a hook for later…
Cactus Demon Impaler: Like I said, once the term "Cactus Demon" crawled into my head, it wouldn’t leave. These guys have a new mechanic, one which I think could be useful for modeling more severe effects in 4e — the "until someone makes a heal check" term for ending a condition. It makes Heal a more useful skill, even at high levels when magic or "inspirational" healing is common, and provides a nice visual — someone’s got to pull those nasty spines out of you! The impaler thus is pretty good at crowd control — he can stop one person dead in his tracks and give someone else a big ol’ cuddle hug of bleeding painful death! These beasties would make nice pets for a summoner NPC, esp. one with a plant and/or desert theme going.