Flayer Leech

A flayer leech is a tiny invertebrate with a semitranslucent body and what appears to be a head that tapers to a point. This head is actually a segmented mouth that unfolds into five petal-like jaws, each lined with row upon row of curved, barbed teeth. Lodged deep within the flayer leech’s throat is a retractable proboscis that, when extended, vibrates at an ultrasonic frequency high enough that it can pierce a creature’s bones, siphoning the marrow inside. This appendage is surrounded by a pair of spinnerets that produce a durable material that is essential to a flayer leech’s life cycle. A flayer leech is approximately 1 foot long and weighs only a few pounds.
A flayer leech is a mindless, opportunistic predator that preys on all living creatures, but when it kills a humanoid or monstrous humanoid, it can wear the skin of its victim like a suit of clothes after a process of metamorphosis. After dragging a corpse to a secluded location (sometimes underground), a flayer leech begins the grim work that inspired its name, using its barbed teeth to carefully cut off the corpse’s flesh in large pieces. The flayer leech then siphons as much marrow as it can out of the creature’s bones, enough to sustain the leech for weeks, and consumes the brain.
Once full, the flayer leech returns its attention to the pieces of skin, using its spinnerets to create a nearly invisible filament and its proboscis like a needle to stitch the tatters back together, exactly as they once were. This filament is coated with a regenerative wax that fuses the flayed skin back together, leaving only barely visible lines. The flayer leech crawls into this fleshy cocoon and pupates within for a few days, developing a bone structure and vocal organs, as well as respiratory, circulatory, and nervous systems similar to that of the victim. It also absorbs a portion of the victim’s memories from the victim’s brain matter and acquires some psychic abilities. After this period, a flayer leech becomes a flayer leech effigy, a convincing simulacrum of the dead creature.
A flayer leech effigy then attempts to insert itself into the dead creature’s life, though close friends might recognize a changed demeanor, as the effigy speaks rarely and doesn’t engage in as many social functions as the victim. In addition, an effigy’s auditory organs are sensitive to sounds that wouldn’t normally harm humanoids of the same type, which can sometimes give away the effigy’s true nature. When threatened, an effigy can protrude larger versions of its pharyngeal proboscis from small slits just below its wrists to defend itself. It also uses these tubes to extract the marrow it needs to reproduce—a disgusting parthenogenesis wherein the effigy belches forth fully grown flayer leeches.