From Introduction:
In the early days of this city, the sorcerer-kings built secret tunnels and basement vaults below their palaces. These cruel regents have all been overthrown, but that is little consolation to the many craftsmen who were buried alive beneath the walls they helped constructed. Their tormented ghosts were absorbed by the remnants of extraterrestrial oozes, summoned to this plane to prosecute the wars of their wizardly masters. Now they are men made of slime, condemned to wander the sewers beneath the city, repeating their routines as if they are still ghosts who mimic the lives they cannot leave behind. Delvers call them sly manikins, because they seem like mere mockeries of life — until they trick you.
Sly manikins are blobs: beings made entirely of slime, encased in a porous purple membrane. They can twist and bend in all many of way, even squeezing themselves through the tiniest gaps, given time. The ghosts they have absorbed lend them some semblance of shape, that of featureless men, though they do not always have to stay in this form. Some shape only a portion of their body into a humanoid figure, in order to lure actual humans into the water where they will hopefully drown, after which the sly manikin will consume their flesh.
In the sewers, they usually feed off other slimes and molds, or scavenge from the refuse thrown down here. Some fi nd sources of magical energy, and use that to sustain themselves instead of organic nutrients. This can backfire, if that energy consumes them instead, but it can also lead to slimes that are even more powerful or intelligent than normal. But those that gain a taste for flesh will not find enough below the ground. Even if adventurers descend in droves, looking for some fortune or other, these “gold rushes” never last long, and carnivores will need to seek out new victims in the world above.
Sometimes a ghost in one of these creatures will “awaken,” regain a sense of sentience. Sometimes it is even multiple ghosts that become one personality inside their slime body. These creatures rarely stay within the sewers, preferring to ascend to the surface world and seek out new opportunities. While their ghosts cannot return to their former lives, an awakened sly manikin could, perhaps, become a sorcerer, or enter the criminal underworld in some capacity.