Shoggoth

Shoggoth is a large, slimy, jellyfish creature that appears in the Innsmouth sewers and in the mission "The Marsh Refinery". It is extremely hostile and attacks Jack on sight.

History
Unlike many other creatures in the game, Shoggoths didn’t originate from the Outer Space, but were rather created and evolved on Earth. An extraterrestrial race known as the Elder Things is responsible for their creation. They “designed” the Shoggoths to be resilient, obedient and shape-shifting, so that they can serve as slaves to their Elder Thing masters.

For millions of years Shoggoths were used as slaves by the Elder Things (particularly used for building underwater cities). The Elder Things thought that the Shoggoths could never evolve to pose any real threat to them; this was the wrong assumption however, as Shoggoths gradually evolved and started planning their rebellion. When the Elder Things were weakened after numerous wars they fought (mostly with the Polyps and Cthulhi), the Shoggoths attacked them. Rebellion was so great that the only way for the Elder Things to quell the uprising was to use atomic weapons.

Very few Shoggoths were left alive, but some of them did manage to escape and hide in the deepest parts of the ocean. There, they soon met the Deep Ones and many of their race entered into a pact with them (although the true nature of this alliance isn’t clear; it is also possible that the Shoggoths were somehow enslaved by the Deep Ones).

Role in the game
There is at least one Shoggoth appearing in the game. One Shoggoth is encountered in the Innsmouth sewers, while the other (probably the same one) is encountered in the Marsh Refinery. The Shoggoth is confirmed to be given by the Deep Ones to Robert Marsh, who then put the creature inside the Refinery, much to the displeasure of his brother Sebastian.