After the gang looked for the two monsters, Shaggy Rogers saw his big fan, Big Green (Green Humungonaut), while Scooby saw his big fan, Big Red (Red Humungonaut).
Big Green started fighting his foe Big Red.
The two monsters were unmasked; revealing that the Green Humungonaut was Max Minner and the Red Humungonaut was Jax Minner.
The Minner Bros. both got mad at each other when they both built their own departments. So they created the Humungonauts to destroy each other's departments. Max would have gotten away with it if it weren't for his meddling brother. (Battle of the Humungonauts)