Treacle

A curious bunny, an abandoned infant, or a delicate songbird can spell slow and agonizing death for the unprepared. Beneath any of these facades may lurk a treacle waiting to feed on a gullible victim, mewling and cooing all the while. Whether by natural selection or arcane tampering, these compact oozes prey on kindness.
Diet of Blood. Treacles feed on blood but lack the natural weapons or acid of larger slimes. To survive, prey must welcome and embrace them, unaware of the threat. The treacles’ soft bodies absorb psychic impressions and take the shape of unthreatening creatures. In the wild, treacles assume the form of an animal’s offspring to lie close for several hours.
Pet Polymorph. Among humanoids, treacles transform into pets, infants, or injured animals. In the most horrific cases, these oozes resemble children’s toys. Treacles don’t choose their forms consciously, but instead rely on a primitive form of telepathy to sense which shapes a potential victim finds least threatening or most enticing. They can hold a new shape for several hours, even if the intended victim is no longer present.
Slow Drain. Once they have assumed a nonthreatening form, treacles mewl, sing, or make pitiful noises to attract attention. Once they’re in contact with a potential victim, treacles drain blood slowly, ideally while their prey sleeps or is paralyzed. If threatened or injured, treacles flee. A sated treacle detaches from its victim host and seeks a cool, dark place to rest and digest. With enough food and safety, a treacle divides into two fully-grown oozes. Rarely, a mutation prevents this division, so that the sterile treacle instead grows in size. The largest can mimic human children and the elderly.
Treacles are small, weighing less than six lb. Their natural forms are pale and iridescent, like oil on fresh milk, but they’re seldom seen this way.