A gibbering mouth is a grotesque mound made up entirely of eyes and mouths. Once they consume a victim their eyes and mouth become a new addition to the nasty thing's body. This would be a good way for your party to gain some renown in the place they're in now. Have them defeat these piles of yuck and see how the townspeople thank them! This could lead into them having a home base type place they can go to when they need to rest and lay low! A good home base is essential to any party! Thanks for listening. Be safe adventurers!