Necromantic Sludge

This black slick of goo is a necromancer's botched attempt at a lichdom potion, poured into the sewers.

Sensing thinking humanoids within 100 yards, it cannot be surprised and hunts them recklessly for their life force. Simply touching it is poisonous, dealing 1 hp per round, and its lashing pseudopod hits for 1d4+2.

When it kills, it soaks into the corpse, whose skin goes ash-gray within a round, and pilots it as a true zombie for a few months, or until a fresher body appears. Armed or not, the zombie hits for 1d8.

It reflects spells like a ring of spell turning, but turns back 100% of any spell or magical item effect. Normal weapons hurt it, though magical bonuses to hit and damage do not count.

It lives in the sewers near the old necromancer's lair, though some has lately spread. Sages guess it is driven by a deathly hunger to end life, or by a lingering need to grant its maker undeath. Groups show some cunning: one lies still in zombie form like a fallen corpse while others lurk nearby to ambush whoever comes to look.

It feeds only on humanoid life force, ignoring animals and other monsters unless attacked. Made of inedible magical slime, it is never eaten by other sewer creatures.