Jerry's Mytholog is a physical representation of the way that Beth perceives Jerry. It went rogue and teamed up with Beth's Mytholog in an attempt to take over the universe. It appeared in the episode Big Trouble In Little Sanchez.
Jerry's Mytholog is a short, chubby worm. It is incredibly submissive, and literally has no backbone, giving it the ability to shapeshift. It moves unnaturally straight, and makes weird anxious noises when it is pursuing someone.