From opening paragraphs:
The spawning pits dungeon assumes that the primary antagonist in your campaign is creating tomb bats. These small creatures fly out into the world and animate dead in cemeteries and on battlefields. If your antagonist is a necromancer, or is working with necromantic magic and the undead, then this asset is an easy fit with your campaign.
It is possible to use this dungeon with other kinds of antagonist, as well. The tomb bats could perform some other function, one that serves the needs of the antagonist better – perhaps they spread plague, or they function as spies, or they hunt out magical items or worshippers of a particular god. Perhaps they are not bats at all – perhaps the process creates
specters or flesh golems instead of tomb bats, or some other kind of creature. Perhaps the process creates a new kind of poison, or a new precious metal, or a special kind of food that can be used to turn humans into halffiends. The tomb bats can be adjusted to serve whatever far-reaching goal your antagonist has. This dungeon assumes only that the process relies on a heavily researched technique and that the vivisection of dire bats is required.