1st level of the dungeon has 4 entries for largely mechanically identical d3 small poisonous critters- Snakes, spiders, scorpions, and centipedes. Also a swarm of regular spiders but that at least has swarm rules. It also has dire rats, giant firebeetles, and stirges, all of which are pretty much 'a 1-hit nuisance' with stirges having their latch on thing and firebeetles having their 'torches' as loot.
Also in the 'can't be negotiated with (probably)' vein are d4 human warrior skeletons and d3 human commoner zombies.
Let's combine all these into ONE thing.
They glow with a sickly radiance that leeches the life from everything illuminated by it, dealing 1 damage to organic beings upon being illuminated and 1 damage upon leaving the radius of illumination. Staying inside he illumination is safe though- your system adapts to the mild aura of death. They also suck blood with their long probiscuses (probiscii?) and lethal hits indicate they've stabbed it into your heart or brain or something. This light makes them easy to see coming, but their maggots also reanimate corpses into glowing zombies, so corpse disposal/recovery is a must.
So- we've got a light source with an exploitable effect, nuisance enemies that aren't worth fighting due to no treasure and an annoying ability, an excuse and boost for the undead, and some pretty good encounters that I bet you wouldn't get from d3 enraged footlong centipedes. Imagine a room illuminated by twilight moths behind crystal- you can charge through and eat the HP tax every time you want to pass through, you can lure enemies here to soften them up, you can break the crystal container and deal with the angry moths. Or a room where the moths flit about a huge cavern over which a bridge is suspended- coming in and out of their light will be lethal unless you have a portable source of Skull Moth light to keep yourself adapted to skull-light. And you can bet the dungeon denizens carry around maggoty glowing skulls for light and damage... speaking of, there are
d3 dwarves, d3 elves, d3+1 gobbos, d4+2 Kobolds, and d3 orcs.
Let's say 'screw that' and have there be 5 groups of 3 humans, all ostensibly fellow adventurers who haven't banded together because of various cultural tensions.
Group #1- Foreigners- Nobody speaks their language, their swords are weird, and their armor is lacquered wood. They have a flag. Invaders? Enemy scouts? What's the deal here?
Group #2- Local Yokels- Clubs and such. Their reaction to you is largely based on your recent exploits in the area. They'll assume you're no good bandits/cultists/foreigners if you have no recent exploits, and won't be impressed. Maybe they survived the calamity that befell the town and are surviving townsfolk.
Group #3- Mercenaries/Bandits- There's not a war on, so they're hoping to get some income with a little tomb robbing. Bad blood with group #4.
Group #4- Local Woodsmen- Here with a hunting dog and a reason. Maybe they're here to lynch some bandits, or look for a missing person. Everyone kinda looks banditish down here though.
Group #5- Demon cultists- Yeah, there's a lot of demons on these encounters. Pretty much just more local yokels, but they want to get human sacrifices for their wicked masters. Indistinguishable from yokels.
Roleplaying, dilemmas, and some factional politicking will be a lot more likely with humans than some goblins would be. The other route I could see with those d3 demihumans would be them being a fellow adventuring party that got split up, but then they're more like unique encounters more than ones you'd be fine with rerolling.
Finally, we have a lemure, which is a sadsack low level demon, a krenshaw, which is like a dog with a really scary face, and a darkmantle, which is a flying squid that drops magical darkness.
Let's turn the Lemure into an Imp. It's a familiar/spy for the cultists and isn't here to fight. Chase scenes! Low-Level Faustian Bargains! Deception! I don't think lemures even talk, so imp is just better.
The darkmantle can be a mutant Skull Moth that flutters around blind because it produces Darkness instead of light, as will its maggots. A huge roiling mass of darkness that drains your life looks a lot scarier than it is, and could complicate things like that bridge mentioned earlier, or other encounters. The moth shouldn't be perfectly in the middle of the darkness either- dealing with this roaming blind spot will take more than a to hit roll at -4 (unless the moth has closed to melee at -4 to hit itself, I suppose).
The Krenshaw should just be a big dog, usually (4/6) chained up. Maybe it belongs to one of the human groups? Or maybe it's just a wild animal. Could be guarding something. Anyone have Speak with Animal? Releasing and feeding it gets you a loyal hound, but you'll need the key. Or you could just shoot it with arrows while it's tied up, but unless you're very sneaky, it's sure to bark and alert others.
Anyway. Having snakes AND scorpions AND spiders AND centipedes won't make for an interesting encounter chart. Having a few encounters that can be different based on terrain, social context, past actions, etc etc... thats what will end up stocking the dungeon with good encounters.
Door+ Moth- You can see the light through the cracks, so you know what you're getting into before you open it. Alternately, doors provide an escape route both from the light and the bloodthirsty insects.
Door+Human- If it's locked, one of the other groups might have the key. Maybe it's just held shut by people on the other side. Maybe they spiked it shut for a good reason.
Door+Dog- It could be a sentry, barking to alert those on the other side. Maybe it chased something TO the door and wants to get through, but lacking thumbs, it can.
Door+Imp- The imp could fly away with the key, possibly trying to lead you into danger. Or maybe the imp wants to bargain for information- it'll tell you which door leads to treasure/where the key is/whatever in exchange for something.
Pit+Moth- A dead, glowing maggoty zombie at the bottom? Maybe a big high-ceiling'd room filled with moths and the pits provide cover to get across. Or maybe they've been breeding in a closed pit trap and opening it will unleash a swarm. A wide pit could be a deathtrap with one bobbing around overhead, bringing you in and out of the light, and you unable to reach it.
Pit+Human-Using a pit as terrain to fight you, trying to trip you in to split the party. 3 dudes with slings could be nasty if they've got pits to keep you away. Maybe they're hiding in shallow pits and ambushing those who come near, or throwing treasure into the pit as idiot bait.
Pit+Dog- A dog in a pit is a pitiable sight, but that's all I got.
Bridge+Moth- Similar to pit. If it's very narrow, the people at the front and back might get swarmed and not have anyone available to help. If things get bad, you might have to jump off in the hope the bottom is safer.
Bridge+Human- If they're threatening to cut it down from the other side, that's a strong bargaining point. Maybe one blocks the way in a none-shall-pass deal. Or just in a toll-bridge way. Just hand over some treasure rather than fight the plate-armored knight 1v1 on a narrow bridge, that's the way...
Bridge+Dog- If you are being pursued by hounds and can't get behind a door, a bridge could be a good choke point
So what I'm getting here is maybe 1 level with some subtunnels and caverns between pits and off bridges- the undead probably lurk down here, and then patrols/scouts of humans trying to catch/avoid each other while managing the threat of the moths. Dogs are generally related to the humans, unless they're feral encounters to befriend or fend off.
I think this place could be an 'above-ground' dungeon- it's a ruined village overrun by feral dogs and rival bands of scavenging humans who are preyed upon by the demon cult and the Skull Moths. Keys are required for the intact structures, which are storehouses and sleeping-areas for the humans. The moths and undead are underground and inside mainly. The town is on a mountain slope and a deep ravine is crossed by a bridge, but access to the bridge is behind a busted up and locked watchtower... something like this
|That's the Ravine in the middle|
Nameless buildings have 1d6 rooms, 2d4 in the rich district. Doors locked, broken, floors collapsing into cellars every so often as 'pit traps.' Maybe there's some actual pit traps in the streets dug by the bandits to catch those damn dogs. The demon cult is in the rich district, and the crystal cage filled with moths was probably set up by them in the gate house. There may be secret tunnels between houses poor and rich (though not from poor to rich, as there's the ravine in the way), it's just the poor ones are more likely to be collapsed earth tunnels and the rich ones are more likely to have Skull Moths and undead lurking in stone cellars. Maybe undead with some coin purses, even, that the other human squatters have been too spooked to take from 'em. The poor district has probably been looted pretty thoroughly and the loot in the rich district has probably been consolidated by the demon cult, so the sort of loot you find is 'rusty lantern' or 'dented pot.' Fighting Human Groups for their equipment may be lucrative. Human Groups also give a good excuse to replace dead characters speedily.
The keep is sorta ruined and can be entered without a key, and that'll be Depth 2. Diving down the ravine takes you to like, depth 5 or something. FUTURE EDIT- Depth 4
There's probably only 15 people in this ruined town total, as well as maybe a dozen feral dogs, though the dog packs are kept on the east side by the locked and moth-trapped gatehouse
4-Mutant Skullmoth- As it is shrouded in darkness, it bumbles about in the day too.
5-Imp- It can fly freely over the chasm and does so to whisper promises of treasure and cult membership
6-Feral Dog, 2HD, may bark and alert other dogs & nearby humans, Skullmoth if Night
Replace a Human Group with ' d3 Skullmoth Zombies' for every 2 groups slain, and replace Skullmoth Zombies with d3 Skullmoths (Night) if the zombies aren't dealt with within a week.
Killing Skullmoths (mutant or otherwise) or the Dogs embolden nearby bandits to move in and replace them, and that can be your eternal cycle of restocking assuming nothing ever changes.