Gagzilla is a giant version of Giggles the Frog, the toon sidekick of Gloomy the Clown.
He made an appearance on the Bonkers episode, The Toon That Ate Hollywood. He wasn't really evil per se. He just wanted to be the funniest toon monster, but he destroyed most of the city while trying to get attention.
Giggles became Gagzilla when Gloomy overloaded Professor Von Drake's humorizer with too much toon humor. The humorizer shot into Giggles' mouth, shooting all that humor into him, transforming him into a giant, comedic monster. He started telling jokes, destroying Hollywood in the process. The police and the National Guard tried to stop him using various weapons, such as tanks and tear gas. But none of that worked. Miranda understands that you have to fight funny with funny. She arranged a chorus line of dancing bananas, which Gagzilla thought was an appealing (a peeling) bunch. He ran toward them, and they took off their peels, causing him to slip on them. Then he had a giant birthday cake loaded with dynamite delivered to him. The dynamite exploded on him, causing him to expell out all the toons' humor, reverting him back to Giggles. All the toons' humor went back to their owners. The toons were happy again. Bonkers complimented Miranda on how she dealt with Gagzilla, fighting funny with funny. Miranda mentioned that she had a backup plan in case her plans failed, but then remembered that she forgot to call off the backup, which was a giant banana cream pie. The pie covered the police. Bonkers said the pie was funny, and he and Miranda laughed.