At the end of Matthew Rosenberg’s Joker: The Man Who Stopped Laughing, there’s a short story where the Joker has an ultimately encounter with Zatanna the magician after he flirts with her too hard. The magician casts a spell on him in her usual backwards delivery, which comes out to “no one else will ever have your baby.” The result of that specific phrasing is that Joker wakes up the next day nine months pregnant.
With this development, Joker decides to go to fellow super villain Doctor Phosphorous for medical help. The doctor agrees to help deliver Joker’s child, but things take a standardly wild comic-book turn when the clown vomits up a blob of mud that morphs into a tiny clone of him. As a huge narcissist, the Joker of course adopts this tiny copy as his son.
This is obviously pretty standard fare when it comes to comic books and the often silly side stories they get into. Most people are probably familiar with the notorious Spider-Man panel in which our friendly neighborhood hero is talking to a dinosaur man about how he could cure cancer by re-writing DNA, but he only wants to turn people into dinosaurs. This is already a bonkers thing to say anyway, but the larger context of the panel is even sillier, as it stems from Spider-Man becoming a teacher at the Jean Grey School of Higher Learning, where he gets a group of teenaged X-Men for pupils. Their first adventure involves not one, but two dinosaur men who are trying to turn everyone else into dinosaurs. DC is no stranger to this either, with plot beats like the Batman villain Floronic Man being decapitated by Batman only to survive because his head was exposed to marijuana, which allowed him to live and later flood the streets of Gotham with cheep weed.
Despite the fact that this is inherently not a transgender storyline, but just some silly comic book bullshit, there are still people freaking out about the comic, with one comic book reviewer calling the scene of pregnant Joker in the hospital giving birth “disgusting” despite there being no actual graphic imagery of birth involved in that panel, just Joker on the bed with Doctor Phosphorus checking under his gown to help with the delivery.