Raiders of the Lost Tomb
One of the most terrifying local legends of Chult involves a mysterious beast called the Uluu Thalongh. This entity was able to possess trees and plants, making their branches into violent weapons. Moreover, it could mimic the voices of previous victims. No one was ever able to discover who or what the creature actually was. The name Uluu Thalongh was granted by a Chultan tribe long since gone extinct. The meaning of the term is equally forgotten.
The Uluu Thalongh was an ancient, massive, intelligent, and baleful monster. Its actual appearance was not known—if it had a normal "form" at all. Instead, the Uluu manifested itself from "within" the trees and plants of the jungle, appearing as bulges and ripples as it moved along.
The Uluu's approach usually came with a strange sound like that of atonal pipes. The Uluu's other manner of sound-making was far more terrifying. It had the ability to sting sentient prey with a sharp root and suck the hapless victim's innards out. With the empty husk that remained, the Uluu was able to control the body and speak through its lips. Using this method, the Uluu would often lure further victims into its clutches by imitating friends or pretending to be a traveler in need.
When moving within the jungle plants, the Uluu could make any branch into a jawed tentacle that would snap and tear and kill until slaying all in a given area. Somehow, the Uluu could locate its prey with precision, even without any sort of eyes.
If a possessed branch were severed from its plant, the Uluu would cease attacking, but it could never seem to be destroyed in this or any other manner, despite attempts by groups of wizards to set fire to large swaths of forest in hopes of killing the legendary beast.