“Just because it's all natural, doesn't mean it's all good.”
Shub-Niggurath or traditionally The Black Goat of the Woods with a Thousand Young is one of few Lovecraft entities that deserves as pronoun other than "it". Shub-Niggurath is consistently and definitively depicted as female, though it is not clear if she has a male counterpart. She is the Dark Mother, the twisted essence of creation and fertility. She is constantly spawning lesser beings of various and seeming random shapes. She may be the ur-source of the legend of Lilith, the first wife of Adam, who was ejected from Eden before the fall. Lilith gave birth to a legion of demons, known as the Lilim.
While Shub-Niggurath is rarely encountered directly, knowledge and worship of her is quite widespread. Her name is often invoked in ceremonies where true worship of the dark gods occurs. Perhaps this means that she listens more than other gods.
She has given a few gifts to her worshippers over the years. Perhaps the most potent is Mother's Milk, though its power is rivaled by that of her Dark Young. Her gifts come at a price, and like any mother, she often gives too much.
Shub-Niggurath's true form is said to be a large roiling black mass that is constantly moving and changing. Gross living things spew out of her constantly, and it is impossible to tell where she ends and where they begin.
There are various groups that worship her directly, some old, some new. Among the old are the Skoptsi, and among the new are various New Age sex cults.