Slithering Tracker [Ooze/Slime/Jelly]

These plasma-draining jellies lurk in dungeons and similar dark places. Not truly invisible, they are simply made of clear jelly, leaving just a 5% chance of noticing one by luck.

A tracker squeezes through openings no larger than a rat's burrow and oozes over any surface in total silence. Because its attack is slow, it targets the sleeping, the unconscious and the alone. Its touch paralyzes for 12 hours unless the victim saves vs. paralyzation. It then covers the whole body and slowly drains its plasma, killing it; a man-sized victim takes one hour.

Trackers are loners, and since none can harm another, territory goes to whoever arrives first. Though the smartest of jellies and slimes, they cannot lead the rest, which lack the minds and means to organize. So they remain low on the food chain, scavengers culling the feeble and foolish while bigger predators take the large game.

Many hide in big monsters' lairs, since such beasts kill more than they can eat. When the owner sleeps or leaves, the tracker drains the leftovers, many merely unconscious until then. More than once, monster slayers left a friend guarding a hoard while they fetched help and returned to find him oddly shriveled, the treasure untouched.

Most likely they are advanced jellies that luckily developed clear plasma bodies and some intelligence, breeding asexually like other jellies when food and time allow. A more dubious theory, prompted by their intellect, says they are made by a hideous transformation of living humans; legends tell of dark wizards stripping enemies' bones to leave shapeless jelly-like flesh. No decent good or neutral wizard would do it, but some dark practitioners have done far worse, and perhaps an old journal in a forgotten wizard's dungeon records the curse in full. Tales also speak of enormous trackers in the deep underworld, fattening on abundant prey at the edges of great subterranean civilizations.