The Jungle Beast was a fearsome mythical creature that was said to inhabit the Flotsam Island jungle. The existence of the creature was confirmed because any meat placed on the altar in the jungle would disappear.
Hemlock's portrait of the beast
When Guybrush Threepwood was after the ingredients to make La Esponja Grande big, he tracked down the beast and discovered that it was actually a carnivorous plant that was able to move.