The Great Devourer in an ancient and extemely dangerous snake that gets bigger everytime it consumes anybody or anything. When it was released from its tomb it ate Gumball and was trying to eat the others but before it could eat them Unicrongot in its way and reminded it about their mission to destroy elmore and then the world. When Gumball's friends escaped they wouldn't do anything but cry but when they thought of an idea on how to defeat it they all snapped out of it.
When they put their plan into action they didn't destroy it but made it weak enough to call in a retreat. After they attacked The Great Devourer it spitted out Gumball and then retreated along with Unicron and Megatron.
Megatron made The Great Devourer promise that it can stay in his group as long as it dosen't harm Teri ever, however, it broke the promise but before it could harm her Megatron got in it's way and faught it, kicked it out of his group, and left it to die.