So compounds have beast/slime/undead minis with construct/gremlin/fiend bigger guys depending. I propose a new area with the opposite pattern, but same "tier 2-3" only and combo behavior.
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Derelict
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A combination of Concrete Jungle and Dark City-like areas that bleed into one another (just the look of it, not related lore-wise, just as compounds do not indicate that wolver dens are connected to facilities), filled with construct/gremlin/fiend minis and bigger beast/slime/undead guys, indicated by a yellow/pink/pale monster icon, respectively. The icon is a similar shape to the compounds, but instead of plants in the corners, it has squares indicating bricks.

Lore could read:
Derelicts were once splendiferous cities. Unfortunately they were designated to dock indefinitely next to mass waste disposal areas due to an error in Clockworks scheduling. Home to the desperate and greedy, those who deny their fate try to keep the streets clean, while others are content to spoil in the junk which spills endlessly down from above.

The streets of these derelict cities are overrun with vermin (think packrats and nasty little pests) forcing a strange evolution... and anything nearby is viewed with the most simplistic, sinister greed. Knights are very shiny! They should be...collected... The more sapient denizens of the Derelict try to keep it clean, and reside in the less filthy "dark-city-like" areas, and reject all they consider to be "unclean," including knights, though over time monsters have become accepted as members of the forgotten society, so we have a dominant mix of chromalisks, royal jellies, and spookats. This combination of attitude results in some very interesting mini monsters and population combinations. Kleptolisks hang out in the junkyard (concrete-jungle-like) areas. Filth includes ash coating surfaces (fire theme), electronic dust as we see in GitM (shock theme), and so on, it's not limited to garbage/poison. It's everything deemed to be "junk" that gets thrown down, including enough plant seeds for them to take root in the rot, hence the similarity to concrete jungle.

EDIT: the cities are always "next to" junkyards, which are far too hazardous for normal exploration due to stuff always falling down from above as well as the endless "sand dunes" of unstable junk, the filth just spreads into the Derelicts next to them. Of course, these junkyards end up spilling their bottoms out to yet more junkyards below, presumably to end up "where they're supposed to go" eventually. Monsters in the Derelict find and carry shinies from the way-too-close junkyard, which knights never actually visit. One man's trash is another man's treasure, after all. The backgrounds of Derelicts could be animations of distant pipes spilling stuff onto barely-seen junk mountains in the distance. The "concrete jungley" parts of Derelicts would have a lot of aesthetics such as broken down mecha knight parts, similar to the Ancient Generator, but much more. They could even sparkle and, when investigated, drop "junk" such as Scrap Metal or Shards and so on.
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Changes to Compounds/How Derelicts could be:

-Mini monsters will not infinitely respawn unless the player walks near/over the busted floor, disturbing whatever was rustling around in there. This potentially causes more than 1, up to 5 to spawn at once. Certain areas are riddled with holes. Beware the mender knockback and lag! Interestingly, a heavy statue placed over a hole will block spawn, if one is around...holes can be triggered to spawn minis an infinite number of times.

-Compounds have a few more boxes, but they are hidden, spawning only if criteria are met, such as pressing buttons. There is already a room like this in compounds, I hardly ever see it. Moar pls.

-All respawning monsters drop a small amount of heat.

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The Minis

Note: scaling down monsters would require some spawn adjustments, so, I'd much rather see new models of course, but here are some options:

Construct: just shrink scuttlebots. They're very simple monsters attack-wise, and they totally look like they could be street cleaners. That fail at their job miserably, based on the filthiness of the place. Alternatively, design tiny rogue Roombas that attack by rushing and exposing blades, a horizontal wisp if you will. What? You need knives to clean things and cut through like a weed-whacker right?!

Gremlin: already have knockers. Little tiny packrat midgets genetically engineered to crawl through vents... Or...gremlin child slave labor? Ew. Rumor has it they form their own clans in the dark depths of the Derelict's sewers, but you can only pronounce them if you gargle said sewer water. Alternatively, use the knocker model but make a "more mini" version that's feral and mindless... Packrats without clothes, or in filthy rags. They swipe at the player with tiny claws, similar to a zombie or retrode, but faster with less dmg.

Fiends: "Puck"
Pucks would be a new monster model. They are simple fiends drawn to Derelicts by the wishful thinking and greed of its denizens. We have shapes - jelly cubes, jelly drops/dust bunnies. Squares and circles. Fiend minis could be a tiny hovering-just-above-the-ground pyramid with an eye on one side. This fits in with irl doubt and "mysterious fiend activities." I've also viewed gods as scavengers, ever since I read Terry Pratchet's "Small Gods," so even the Eye of Providence fits here. It's also an allusion to Bill Cipher from Gravity Falls, a demonic entity bent on bringing destruction through portals. Which is what certain fiends do in SK. The side with the eye would lock on to a target, always facing, widen/charge up, and hover-chases after the target. Idle pyramids with no target rotate in place with the eye closed, and otherwise do not move, adding to their creepiness. Attacks are simple: the eye charges up and releases a short-range burst of purple shadow energy, dreadfully shaped similar to the ghosts spawned by the maskeraith's "hexing haze" ult. After firing this weak spirit summoned from who knows where, the pyramid wobbles in place as if from knockback and squeezes its eye shut for a second before charging again. Same attack speed/strike attempts as bunnies, roughly. Coincidentally, devilites use pucks to play street hockey during what little spare time they have, with the idea that a pyramid which hovers over the ground on its own is a prime economic choice (think like air hockey), and the pointyness is better than a disc in case someone trips onto one. Puck is also a mischievous fairy, so I feel this name fits very well. It's a simple word to fit in with minis, who are more mindless than most other monsters, driven by simple needs. Default color for the Puck would likely be a dark grey/purple/blue, as devilites/greavers/gorgos are.

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TL;DR: New area, "Derelict," that is essentially a combination of Dark City and Concrete Jungle, while associated with the lore of neither, following the stratum and level generation parameters that Compounds do. New mini monsters for the construct, fiend, and gremlin families could be introduced to balance the current compound pattern.