The Humorizer was a device invented by Professor Ludwig Von Drake originally meant for the process of "Humorization"; to refresh a toon's sense of humor.
When Gloomy the Clown stole the humorizer, he used it to suck out a toon's sense of humor, because he wanted to be funnier than the toons. Any toon zapped by it starts crying endlessly.
When Gloomy overloaded the Humorizer, it started shooting out of control and flew right into his sidekick Giggles' mouth. It shot all the toons' sense of humor inside Giggles, transforming him into a giant frog comedian named Gagzilla.