The Gibbering Mouther is an original monster in the Dungeons and Dragons game. (My information will be from Dungeons and Dragons Third Edition, as the SRD gives us full permission to use this information.) The mouther is a slithering protoplasm comprised of slime, mouths, and eyes. In addition, they constantly gibber, which causes intelligent beings in the area to be affected by a confusion spell. (Confusion in D&D isn't just "Huh, what?" but an affliction which can cause you to attack your companions.) So, in essence, the mouther says things that make you go temporarily insane. In addition, they can release a stream of spittle which ignites in contact with the air. This causes a blinding flash of light. (Now you're confused AND blind.) If that wasn't enough, they can control the ground and stone around it to have the consistancy of quicksand. Now, you're blind, confused, and stuck to the ground.
Their attack forms are nasty, as these are just their "Keep you busy so I can eat your nice juicy paladin friend" abilities. They can grab you (improved grab), drain blood on a successful grab (which causes constitution drain), and finally just plain out engulf you if you're small enough (medium size or smaller, basically human size or smaller). Since they're blobs, they have no particularly vulnerable points, so they're immune to critical hits. Since they have a ton of eyes, they get a bonus to spotting things. And since they have a ton of flexible mouths, they can shoot out up to 6 mouths to attack at a time (and each can grapple and drain blood).
All of this fun and excitement, however, has a mere 22 hit points on average, so a reasonable wizard could remove this threat in an instant. Placing this love and attention at a mere challenge rating of 5. Throw one at your players, they'll love you. (Strangely enough, these things are able to speak in common tongue ... and even odder, they have a Charisma of 13. I have yet to figure out why that is!)
More information is available in the SRD, under the "G" section of monsters. We love the SRD! | 
