Proto-Shoggoths are a subspecies of shoggoth.
There is a theory that the Elder Things created life on Earth using the proto-shoggoth. However, according to the Book of Eibon, it was Ubbo-Sathla who created only terrestrial life. It is possible that the explanation for this inconsistency is that the proto-shoggoth was created using genetic material obtained from the plasma remains that Ubbo-Sathla left on the surface. Therefore, the proto-shoggoths would have arisen from Ubbo-Sathla and subsequently all life would have arisen as a result.
Modern recreation Edit
According to The Madhouse: And Other Stories (the Call of Cthulhu RPG manual containing the story "The Madhouse"), Dr. Terence Freygan began creating an army of proto-shoggoths after studying a Greek copy of the Pnakotic Manuscripts in hand from a local cult of the Silent Shouter of the Hills and having studied the case of Jeffry Quarren, a boy abducted by the Great Race of Yith who maintained a mind of these beings. Since then, truck fleets have approached the Greenwood Madhouse, the doctor's workplace. And, time later, there were a series of deaths around the madhouse. The reason behind these events is that Freygan, using the manuscripts and a laboratory built in the building, began to transform human tissue into proto-shoggoth fabric using a catalyst in the asylum patients. These attempts resulted in the death of the patients, but subsequent attempts maintained the brain, which spread throughout the body. The doctor came to use himself as a guinea pig successfully, but he still seeks to refine the process to turn the cultists and the nearby people into an army of these protoplasmic beings using a series of medications alongside the use of the catalyst.
NOTE: taken in part from Dr. Freygan's description according to "The Madhouse".
Proto-shoggoths have an elastic and metamorphic body: they can suddenly extend an arm over distances of up to three meters or look by just forming an eye in the palm of the hand. They take minimal damage from physical weapons and cannot be impaled (having no internal organs). Fire deals only half damage to them, and has regeneration. They don't need sleep. If a proto-shoggoth becomes nervous, there is a chance that he will lose control and his features will deform revealing his non-human form. So, you cannot change your features to look like another person effectively, but you can keep your old human form or be monstrously deformed. In the monster form it has the same color and texture of human skin, although it is mobile and can change shape at will, growing limbs, sensory organs or mouths without lips. Now its total mass and volume cannot change, so if you make a long, thick arm sprout from your chest, some other part of your body will shrink equivalently.
In combat, in addition to body movements (such as punches, firearms, prey...), they can use a crush. Unlike true shoggoths, they can only attack one human victim at a time until death by crush or absorption.