I gotta say, the first time I stumbled across a Joker mpreg fic, my brain just blue-screened. Like, of all characters? But then I actually read one, and the logic some writers use is weirdly airtight if you accept the premise. It’s rarely just ‘he gets pregnant.’ The setup is everything. I saw a fic where he was exposed to a modified version of Scarecrow’s fear toxin that had bizarre side effects, rewriting his biology as a twisted joke on Batman—creating life from chaos. Another one used magic, a relic from some gala heist gone sideways. The key is anchoring it in the specific version of the Joker; a 'Gotham' TV show Joker has a different vibe than a 'Dark Knight' one. They lean into body horror, the grotesque comedy of his situation, or sometimes a terrifying, obsessive fixation on this ‘project’ that’s both deeply disturbing and oddly in character.
A lot of the tension comes from how the Batfamily reacts, especially Batman and Harley. Does Batman see it as a medical crisis to be managed, another victim to save? Does Harley oscillate between horror and a twisted delight? The best ones don’t shy away from the sheer absurdity but play it completely straight within the story’s internal rules. It’s a high-wire act, but when it works, it’s a fascinating character study on creation, ownership, and madness. My favorite detail in one was him meticulously painting a nursery in Arkham with graphic, violent murals.