I thought I'd add a periodic Cthulhu monster profile every so often. Excerpts are taken from the Malleus Monstrorum.
On Shoggoths

Created an unbelievably long time ago as tools by the Elder Things, They may not have been even truly intelligent, simply cunning and able to learn. However to the horror of the Elder Things, it seems they were able to learn and evolve.
A shapeless mass of black protoplasmic bubbles, faintly self-luminous forming and unforming all manner of eyes, mouths, and limbs. The sight alone of such a massive terror can tear the sanity from a stable mind. It covered an area of over 5 meters, absorbing all life it chose. The few remains found of its prey, were mere rag dolls of flesh and crushed bone the result of indesribable rupturing, crushing, and being sucked to pieces.
Shoggoths are able to live and adapt to nearly any enviroment from the deep pressures of the ocean floor to the intense cold of the Artic. Some have been found in service of the Deep Ones but they are surly servants at best becoming more and more intelligent through the ages, more and more rebellious, and more and more imitative.
The great Justin Barnes a remarkable scholar of ancient lore discovered fragments which suggest Shoggoths of emmense age could and may have become unusually intelligent and purposeful to the point of controlling his shape and passing for other sentient humanoid life.