The Gibbering Mouther is not regarded as an evil creature, but in order to sustain its mad self, it must feast upon the bodily fluids and sanity of mortal creatures, preferably intelligent ones. It attacks by spitting strings of protoplasmic flesh which end in a mouth and one or more eyes at opponents, which then bite them, causing both acid and blinding damage. When it has defeated an opponent, it swallows them whole, and then proceeds to suck the bodily fluids and sanity. It is possible for the victim to cut their way out.
Having so many eyes, gibbering mouthers are difficult to sneak up on.
Gibbering Mouthers can speak Common, but seldom speak anything other than mad babble and gibberish.
They are regarded as neutral in alignment, but have distinctly evil habits.
Gibbering Mouthers can produce a constant gibbering that confuses all creatures within 60 feet. They can also change nearby ground (whether earth or stone) to the consistency of quicksand. The Mouther can move unimpaired through the quicksand.
A Gibbering Mouther can loose a stream of spittle that ignites on contact with the air, temporarily blinding creatures within 60 feet.
The Gibbering Mouther is very likely inspired by the monsters described in the works of H.P. Lovecraft.