Deathcoil

When powerful rituals of necromancy are performed, it leaves permanent scars upon the world, areas where anything that enters it rots at an alarmingly fast rate. Nothing should be able to survive this. Nothing is known to be able to survive this, aside from people equipped with layers of protective magic. But somehow, Deathcoil thrives in these places, feeding off the decaying corpses of those it captures in its grasp.
Deathcoil is a vine, or tendril, or tentacle, that can be found within the ground beneath a necrotic field. If one could see through the thick mist that coats the ground in such places, one would see a network of dark tendrils, no more than 5cm in diameter, strewn through the area. Here it lies, passively absorbing water that flows into the field and feasting on whatever nutrients can be found within.
But this is not enough to sustain life. The vines are sensitive to sound, sensing the vibrations in the air. When it senses quiet sounds, such as the approach of a creature, it retreats, pulling itself into cracks in the rock below, leaving behind the a faint scent of not-so-fresh meat. This draws scavengers in, hoping for a quick meal. Once a louder sound is heard - a heavy footfall, an exhalation of frustration - the tendrils strike out, entwining their victim and pulling them to the ground. With their prey bound, they simply wait for the field of decay to take effect, and in a matter of moments the corpse begins decaying into a wealth of nutrients to be absorbed.
Nobody has ever lived to report the existence of Deathcoil. Most fear to tread anywhere near the fields of decay they live in (a highly rational fear that is generally encouraged by more experienced adventurers). Even Caelester's Guild of Nightsoil Collectors, which uses the field beneath the city to process waste into valuable Naphtha knows little of their existence - far too little. Some guild workers have been lost to Deathcoil attacks, but all the guild really knows is that, for some reason, making noise while within the field leads to accidents.

Future events

The deathcoil tendrils under Caelester are growing beyond anything typical of the species. With the Nightsoil Collectors unwittingly fertilizing the whole area, they have an abundance of nutrients. Perhaps this will render them increasingly passive - a well fed beast may well be docile...or perhaps the time will come when they grow beyond the field, stretching upward, seeking more.