Small bladdery and bloody clump of tissue.
This repugnant organism can on occasions be seen floating in the rivers of Acheron and Lethe.
There it feeds on the rotten and dissolved bodies of those who have met their demise on the banks of the vile fluxes of doom.
Ultimately these floating cocoons burst open, giving birth to the very creatures you have been slaying in these mazes.

Spirit tech must be one grisly business...