Cistern Fiend

Surging out of the water that concealed it, a giant, translucent green worm confronts you, its large clumps of pinkish tentacles writhing on either side of its body just below the snakelike head.

Tactics
Cistern fiends attempt to paralyze their victims with their tentacles so that they may more easily use their bite attack. They rely upon their coloration to appear invisible when submerged. The creature‘s tentacles secrete a highly toxic fluid from sacs located in the base of each tentacle, and repeated hits from the tentacles will numb and eventually paralyze targets. The cistern fiend attacks paralyzed targets using its bite, which it uses to drain bodily fluids from its target at a horrifying rate. The creature also has very basic psionic abilities, which it uses to repel other creatures from the water supply it protects, while shielding its mind from attack.

Description
Believed to have been bred by some forgotten king or conjured from the twisted mind of a long-dead sage, cistern fiends were originally intended to guard and purify sources of water. Since then they have spread and are now a hazard that can be found throughout the Tablelands.

The cistern fiend, also known as the water worm, feeds in two different ways. It either kills and eats the occasional prey that enters the water source where it dwells or it feeds on a more daily basis by filtering nutrients from the water supply through its mouth pores and gaining sustenance from the minor biological and mineral impurities in the water. For this reason alone cistern fiends are beneficial to any community's water supply. Creatures slain by the cistern fiend have their body fluids filtered by the fiend, with the resulting pure water being expelled into the existing water supply. Cistern fiends are hermaphroditic and reproduce asexually once every decade, with the offspring growing inside the membranous tissue that comprises the fiend's body and emerging through an eruption in the outer skin layer. Docile during delivery, the adult must be separated from its child after birth as no two cistern fiends can share the same water supply without the larger attacking the smaller.

A cistern fiend must remain immersed in water, or it dies after 10d4 minutes. The creature's size depends on its age and the amount of water available, but most cistern fiends average 40 to 50 feet in length.