Impersonator

At rest an impersonator looks like a puddle of thick, stagnant water, though it is far denser and closer to heavy oil. When it hunts, it takes the shape of someone it has fed on before. In its true form it shows no sign of communicating at all, but in a borrowed shape it can use any means of communication its victim had.

Its favorite trick is to wear a welcome face, lead people somewhere they feel safe, and revert once they sleep or are otherwise helpless. It avoids fighting in disguise, since wounds now mean less blood later and the disguise is only skin deep. Whatever it seems to be, it keeps its own 5 HD and AC 8, so a fearsome knight in field plate is nothing of the sort. In borrowed form it attacks for 1d4 and gains none of the victim's special powers, such as spells or infravision, though it does know everything the victim knew.

It feeds slowly, so it must immobilize prey first. Touching its true form requires a save vs. poison at +4, and failure paralyzes the victim until 1d4 rounds after contact ends. It then flows over the victim and siphons blood painlessly for 1d4 damage each round; the only sensation is a creeping, bone-deep chill as death approaches.

Taking a new shape requires one round, and only creatures it has fed on can be copied. It can hold that shape for 1 turn per point of damage it drained from that victim, so 50 hit points taken from a 9th-level fighter lets it be that fighter for 50 turns, about 8.3 hours. It may shed the disguise whenever it likes, melting back in one round. A used form is spent until it feeds on that person again, but a typical impersonator has 3d4 forms in reserve and can use them in any order.

It is cunning and wicked though not truly sentient, and it instinctively senses which of its stored shapes a nearby group would welcome; it will never approach elves wearing a snarling orc. When it finds good hunting, such as a small village, it kills one unsuspecting local, takes that face and joins the community to choose its next meal. By changing faces as it feeds, it stays a step ahead of those hunting it, leaving pale, drained bodies behind.

No one knows where impersonators come from. If they are natural at all, which most sages doubt, they may be related to mimics. More scholars suspect a lower-planar origin or a twisted magical experiment.