The Placental Simulacra was a gift from the heavens, or possibly a curse, depending on who you ask. We recovered the first from a Downington sphere, while the others we either captured in dimensional fatigue events, like the wreck of the INN Hoshijiro. The rest were created artificially by inducing mitosis in the existing samples.
We've decided to identify the test subject as Minerva, after the scientist Dr. Melissa Minerva. The entity Minerva looks like it was previously a cladoceran type planktonoid before it killed and consumed Dr. Minvera. After this, it appears that the creature underwent a rapid hybridization, and has replicated a rough approximation of the Doctor, most notably her upper torso, head, and one arm. The rest of the mass of the creature is the normal looking smooth sphere, with a mass of cilia underneath. It is largely immobile, speaks in a shattered fashion, indicating that it has some of the doctor's memories, but none of the comprehension. If approached, Minerva becomes agitated, and then aggressive. The test subject can be controlled through the application of audible sonic frequencies, classical music, and halon gas.
Placental Simulacra largely resemble humanoids, having the semblance of limbs, a vestigial head, and other traits that are humanish. There is no mistaking a placental simulacra for being human, as they are typically crusted over with rough or rugose tissue, appearing cancerous, covered in horn like chitinous extrusions, or some other monstrous appearance.
The Placental simulacra is a space planktonoid that for unknown reasons, has emulated a human appearance. This generally only occurs after a planktonoid overpowers and consumes a human being. Most of the time after this, the human becomes nothing more than food for the creature, but rarely, the planktonoid will undergo a hybridization. These placentals are biological duds, after fusing with a human, the creatures lose their plasticity, and are usually easy prey for space marines or hunter killer droids.
It was discovered that Placental simulacra can be used as incubators. The entities can be induced to reproduce, and like cells or primitive organisms, they can replicate themselves, but slowly and inefficiently. Such a thing outside of a lab would likely to destroyed and devoured by other planktonoids and hunters before it could really accomplish anything. A tainted sample lead to the discovery of the Chimera. A placental simulacra implanted with a human embryo will function as a birthing unit, bring the fetus to term and then birth. This practice is limited, since the birthing typically destroys the simulacra, or the chimera devours the simulacra after birth. Such things... such things shouldn't be.
The Placental simulacra is a background piece, something to be found in a containment unit, or in a bioreactor, where it is being used to manufacture monsters or raw organic materials. It is the sort of thing to be found in a mad scientist's lab, or in the research department of a callous tech company.
Horror: Placental simulacra can be created, so long as there are people with the means to secure a larvae and are also willing to feed it people until it undergoes hybridization. The placentals do retain something of the human victim, such as the ability to speak certain words, mimic old behaviors and skills, and recognizing people they once knew. This is a frighting ruse because the human is gone, devoured, and it is still a larvae and will act accordingly, and will attack and attempt to consume people who get too close to it. Note: only female victims will create a placental simulacra. Male victims can create a similar simulacra, but it lacks gestation ability, and the end result is a tad bit more hentai.
Echidna: a veritable mother of monsters, placentals can be used to create one of a kind monsters, Alien style.