At one time, the Thin Men were the most advanced infiltration units available to the aliens. Now, we face a species capable of mimicking the human form at will. If we can come to understand how it is that they emulate us so effectively, perhaps we could develop a tool to deceive them ourselves.
I'm at a loss for words to describe the difficulties we've had in attempting to handle this creature, affectionately known as the Faceless by our troops. The nebulous form of its physical structure, including a pliable, semi-solid outer layer, seems to be slowly degrading now the creature has expired. There is also a pungent odor that only seems to grow stronger as time passes.
Early reports from the resistance referencing an alien creature said to be capable of "shapeshifting" were initially dismissed by local cell leaders who attributed the sightings to combat stress and malnutrition. It wasn't until our own forces engaged with the creature that we successfully confirmed its existence. Surprisingly enough, the description of the creature from those early reports was quite accurate.
With a varying height of up to three meters, the specimen currently refereed to as the "Faceless" has one of the most unusual internal structures I've ever encountered. Where one might expect to find a skeletal foundation, we instead see a series of malleable chitin-like structures providing various points for the expansion of several equally unusual fluid membranes.
The membranes in question are responsible for the Faceless' extraordinary ability to mirror the form of a human. In recirculating key cellular combinations via an elaborate internal structure, the Faceless is capable of forming solid shapes while also mirroring colors and textures without physical sampling. As of yet we've only seen evidence of the Faceless attempting to imitate humans, but not other species or inanimate objects. Whether or not this is a limitation of their genetic makeup, or an intentional manipulation of their abilities by the aliens, we cannot say at this time. R. Tygan.