And so the challenge:
1) Take your three favorite human-ish monsters out of the Monster Manual and they are minority citizens in the city. Detail how they get along, how being in the city has culturally changed them and what niches they fill in the city. How do the powers that rule the city keep them down?
2) Take three really bizarre fucking monsters and figure out how they exist in the nooks and crannies of the city and how the powers that rule the city keep these beasts from doing unacceptable amounts of damage?
Methodologically driven by pulled books from my shelves and seeing where they fell open (mostly).
My races: Kuo-toa, Yakfolk, Farrow
My monsters: Wang-liangs, Harpies, Ettercaps
A mountain side city, ancient pride of the wang-liangs, once built atop a glacier now sinking as the ice age passes into memory and the light of the sun grow stronger. Glorious vaulted halls, once open to the cleansing winds of the mountain winters now tip and slide into the melt pools. Decorations of ice have melted away, leaving no trace on blank stone. The austere beauty is sullied by vegetation, the presence of birds, the scuttling life that has come up from the fetid forests below.
Now the city slips into the melt-lake beneath and new inhabitants have come to claim it. Some scant resources come from beyond the mountains, expeditions from the kingdom of the yakfolk to keep this foothold but so far ventures down into the forests have not justified the trouble, where they have returned at all.
Three humanoid minorities:
Kuo-Toa (Monster Manual v3.5) have colonised the city, journeying up through the underdark and finding these structures now submerged in the icy lakes. They produce most of the food for the city, keeping fish and cultivating reed beds painstakingly carried through the deeps below to cleanse the run off from the city. The fresh water seems plentiful but is rapidly becoming full of kuo-toa and the filth from the city. Nominally free inhabitants of their lakes, the elders are beginning to consider easing the burdens of foul water by culling the others who live in the city.
Yakfolk (Monster Manual II 3e) have crossed the mountains as the sun melted the ice, first to bring battle to their ancient foes the wang-liangs then to conquer in triumph as their opposition chose to abandon their melting home. This place is too crooked and tilted, damp and austere for the yakfolk and there is argument over how much effort to put into shoring it up enough to make it a proper monument to their glory. While there is room enough to properly allow every yakfolk to be a royal in their own palace, it lacks the gardens, pleasures and competent vassals of their home cities. The yakfolk who have remained here have tended to be the ambitious and the driven and the plotting and scheming for dominance occupies most of their time while the city continues to sink. With their skin-walking ability they are completely aware of the plots of the kuo-tuo and the farrow and intend to make harsh examples of the first to step out of line.
Farrow (Monsternomicon v3.5) brought by the yakfolk to do the work they will not dirty their hands with. For them this is a miserable cold place, with little fuel for heat, not much to eat beyond the soggy fish they trade their pay for with the kuo-toa. Most of the farrow spend their days in work projects assigned by one or another of the yakfolk, often to spend the following week on another project working to stop the aims of the first. Years of this has plunged most of the farrow into despair, with no chance of returning home over the moutains. The small minority of farrow who scout the surrounding land and hunt for food have seen the space available for escape and a small trickle of 'hunting accident' survivors are beginning to form free villages in the woodlands down slope.
Wang-Liangs (Oriental Adventures 3e) lurk in the depths of the cities, those that have not already departed in disgust as their city sinks and the interlopers refuse to simply die. These that remain in the cool and shady depths talk to one another through their innate telepathy, moving less and less for fear of attracting the attention of the yakfolk. All are hunted by the yakfolk, engaged in an endless game of cat and mouse. Those that remain are the most affronted, ever less likely to leave, remaining simply to soak their claws with the blood of yakfolk.
Harpy (Monster Manual v3.5) joyous predators of the sodden margins where the city, has begun to slip beneath the surface they roam these happy hunting grounds, snatching kuo-toa from the pools or unwary farrow that stray to close. Both the kuo-toa and the farrow have set up shrines and leave trinkets and food to appease the harpies in the hope of being ignored. The harpies find these antics amusing and have no intention of stopping.
Ettercap (Monster Manual v3.5) the reason that the farrow escapees have not fled further than the local woodlands, these spider horrors have even migrated into the city itself to prey upon the plentiful humanoids. They have been tolerated by the yakfolk as a useful instrument of terror - both to assassinate rivals and to keep all but the most courageous farrow terrified of what lurks beyond the city limits. They keep a careful distance from the wang-liangs, recognising the scent of the old masters of the city.