Complex sentence: Mung prepares to execute Scrooge and Launchpad as well, but just then, Bubba arrives, riding on Tootsie, and nearly everyone believes him to be the so-called "Great One".
Split into simpler sentences: Mung prepares to execute Scrooge and Launchpad as well, but Bubba arrives riding atop Tootsie. This astounds and nearly convinces the crowd that Bubba is the so-called "Great One".