Cistern Fiend

Legend holds that some long-dead sage dreamed up this horror. Thirsty travelers who think they have stumbled on an unguarded cistern or well often never have another conscious thought. The cistern fiend is a giant, faintly green, see-through worm with a hideous mouth ringed by a mass of coiling pink tentacles. Fully underwater it is all but invisible. How big one grows hinges on its age and the volume of its water, but most are 40 to 50 feet long.

The fiend bites, and on a hit sucks out the victim's bodily fluids through its proboscis, draining a quarter of his normal maximum hit points every round until he reaches 0 or the fiend is killed. At the same time it lashes with the dozen 10-foot tentacles around its mouth, each fed by a sac of paralyzing venom at its base. A creature struck must make a Constitution check. Failure means the heart stops and the victim dies; success means paralysis for 1d10 turns. The fiend automatically hits a paralyzed creature with its proboscis and drains it, so unaided victims die in four rounds.

Because it is so hard to see in water, opponents suffer -3 on surprise rolls, though detect invisibility reveals it. Its simple psionic powers serve mainly to drive other creatures away from its water and to guard its own mind.

All of its powers are telepathic. Sciences: psionic blast, mind link. Devotions: mind thrust, contact, intellect fortress, ego whip, thought shield, inflict pain, mental barrier, synaptic static, life detection. Life detection is a special ability with no cost.

The cistern fiend, also called the water worm, feeds in two ways. Day to day it strains its home water through pores in its mouth, living off tiny biological and mineral impurities, which alone makes it a boon to any community's supply. It also kills, as described above. To it, every creature is an intruder and a source of more fluid for its pool: it filters a victim's body fluids and releases clean water back into the reservoir.

Out of water it dies in 1d4 turns, which is why it defends its supply so fiercely. Each fiend is hermaphroditic and produces a single offspring by itself once a decade. The young grows inside the membranes of the parent's body and bursts out through the skin. For this 24-hour birthing the parent becomes docile, but if the young is not taken out of the water by the end of that time, the parent kills it. Towns and cities guard their water closely while this is going on.

The fiend may have been bred by some long-forgotten king for one purpose only: guarding and purifying stores of water. Specimens are sometimes stolen, probably as newborns, and can turn up in any sizable body of water. If two adults share the same supply, the stronger kills the weaker.