The halsora is the metamorphic rock of fleshwarps—twice transformed into a creature with completely new characteristics. From humanoid to plant to now a hulking (as much as a Small creature can hulk), acid-weeping aberrant thing, halsoras are the stocky hunting dogs of their drow makers and masters.
I’m curious about the halsoras’ self-hatred as described in the Bestiary 4, because you rarely think of plant creatures, even superficially humanoid ones, being so intellectually/emotionally/spiritually driven. But maybe that spiritualism is the root cause (no pun intended, I swear). Halsoras have been divorced from both their vegepygmy bodies and from the birth bodies they held such reverence for (and likely took mementos from). What's worse, they have lost their connection to their communities and the russet mold patches that linked them together. Instead they feel the mutated spores coursing through them and hate the weeping infection they are powerless to step. It’s tragic, really…or would be, if they weren’t already body-stealing nightmares in the first place.
A drider lurks on the outskirts of a subterranean settlement, obsessively tending her “garden” of halsoras among the piles of trash. The mask and coverings she wears to protect her from the aberrations’ acid and spores have given rise to tales in the community about ghosts, clockwork creatures, and scorpion knights.
The small nation of Ilvdeep is run from below the surface by drow mages and warpriests who reject their kin’s demon-worshipping ways. That doesn’t make Ilvdeep drow any more peaceable, however—they rely on the Houndmasters (half-drow rangers, slayers, and sorcerers) and their Hounds (trained halsora shock troops) to keep the fearful populace in line.
A besieged city needs hardy warriors, and adventurers find themselves pressed into service. As they reluctantly go about missions on the defenders’ behalf, they discover a mad plan by one of the army commanders to create more powerful troops: first by infecting peasants with russet mold spores, then by fleshwarping the resultant vegepygmies into halsoras. The commander firmly believe his actions are justified and that history will laud his actions…but just in case he sends his halsoras to silence the adventurers before they can go public with his plot.
—Pathfinder Bestiary 4 104
Resurrecting Darth Maul as a drider wasn’t my favorite move The Clone Wars TV show made, but it gave me an adventure seed at least. Meanwhile, if you like drow-controlled surface nations, Forgotten Realms’ Dambrath is another candidate for adventure. (Shining South has some details— while it didn’t officially make my Top 18 list, I did give it some love and it's still a book I’d recommend to both D&D and Pathfinder fans alike.)
Sing it with me now: “Halsora, sora… Whatever will be, will be…” I’m going to Hell for that, but TOO LATE! It's in your head forever now.