Hmmm, I like aspects of both (I guess you cross-posted). Let's see if I can merge them (BTW, "king of mouthers" was just poetic license

):
The amalgamated version looks pretty good, although it has a few grammatical errors. I'd like to make the "jungle tribal mouther" version the default.
Oh, and the Scarlet Brotherhood isn't in the
Forgotten Realms, but the
World of Greyhawk.
How's this...
A greater gibbering mouther is an extremely rare form of gibbering mouther. These creatures
thrive on attention, and thus often lair on the outskirts of humanoid society.
Greater gibbering mouthers are
usually found ruling tribes of primitive humanoids deep in the jungle, but
occasionally lead hidden cults of worshipers in the midst of towns or cities.
Their need for worshipful service drives them to split off tiny portions of its own flesh to create parasitic creatures called gibberspawn, which can influence any creature they are attached to. Some greater gibbering mouthers are so reliant on their followers that they have lost the ability to hunt for themselves.
Unlike their lesser kin,
when a greater gibbering mouther reproduces it does not form two smaller versions of itself by asexual fusion; rather, one part retains the essence of the original and the other becomes a normal gibbering mouther.
A greater gibbering mouther is about 10 feet across and 8 to 10 feet high. It weighs about 6000 pounds.
Greater gibbering mouthers can speak Common. Greater mouthers often speak gibberish like regular gibbering mouthers. Their followers go to great effort to interpret the "divine messages" hidden in their master's gibbering utterances. Greater gibbering mouthers will speak coherently when it suits them, mostly to demand food, treasure, and worship.
COMBAT
A greater gibbering mouther attacks by shooting out strings of protoplasmic flesh, each ending in one or more eyes and a mouth that bites at the enemy. A mouther can send out a total of six such members in any round.
If a greater gibbering mouther has any gibberspawn or humanoid worshipers in attendance, it will always send them into battle first rather than risk its own existence.
IN OERTH
The only known greater gibbering mouther on the
World of Greyhawk is Xuxeteanlahucuxolazapaminaco, god-king of the Amedio nation of Chetanicatla. Larger and stronger than others of its kind, it considers itself a god.