Misinformation about climate change is a consequential societal issue, causing polarization and reduced support for climate action. However, the seriousness of the problem does not preclude non-serious solutions. There are numerous potential benefits to humor as a strategy to counter misinformation, such as attracting attention and engaging disengaged audiences. This paper describes a humorous serious game--"Cranky Uncle"--developed in the U.S. to inoculate players against climate misinformation. The game combines psychological research into active inoculation, critical-thinking work on misleading rhetorical techniques, communication research into cartoon debunking, and gamification. The game's cartoon humor and the creative potential of active inoculation lends it to classroom applications; educators have thus used classroom activities to complement the game in order to improve students' climate literacy and critical-thinking abilities. We present several qualitative U.S.-based case studies, in formal English-speaking tertiary classrooms and informal public education settings, to illustrate the utility of a humorous, game-based approach to building resilience against climate misinformation. The approaches adopted in our case studies are offered as a model for other educators looking to use interactive games to teach critical thinking.