Invader ZIM (2001)

Season 1: Episode 33

When Zim attempts to taint the Earth’s cow-meat supply with sewer water is ruined because of Gir’s antics, he decides to increase the power on Gir’s behavioral modifier, which will permit him to stay in serious mode all the time. However, when the serious Gir starts to consider Zim a threat to the mission and runs off to learn things on his own accord, it’s up to Zim and Squidman to find Gir and turn down the power on his behavioral modifier before too many individuals see them and jeopardize their mission.