Among the many crimes one can lay at the feet of the night hags, the worst is their propensity for stealing souls bound to the Shadowfell. They warp their prisoners into squirming maggot forms called larvae, stuff them in bags, and slip away before anyone notices their villainy. The night hags use the larvae for their own dark rites and as currency for payment to other fiends in return for their loyalty or services.
Effect: A larvae pool covers a 2-square-by-2-square area and is difficult terrain. Any creature that ends its turn prone in the pool cannot crawl or stand up (save ends). Each time the creature fails a saving throw against this effect, the creature takes 5 damage per tier.
Usage: Larvae pools are found anywhere night hags are likely to haunt and might be guarded by demonic or devilish soldiers and brutes, especially those that can knock creatures prone.
Published in The Book of Vile Darkness, page(s) 2-28.