Spoiler Warning for Batman: Three Jokers #3
With the Joker's origins as mysterious as they are, one element that rarely gets questioned is the chemicals that first transformed him into what he is. What chemicals Ace Chemicals produced, how they work, and what exactly they do are mostly kept vague. Apparently, these chemicals are responsible for the Joker's sociopathy and clown white skin, but in a new issue, the Joker speculates the chemicals have other effects. In Batman: Three Jokers #3 the Joker reveals that the chemicals which transformed him can cure cancer.
The Three Jokers miniseries sees Batman, Batgirl, and Red Hood trying to solve the mystery of how there are three Jokers. Their investigation eventually leads them to the man who killed Batman's parents, Joe Chill. Chill is dying of terminal cancer in prison when Batman finds him. Later, the Jokers abduct Chill as part of their grand plan to create a perfect Joker. Their reasoning is that Chill's role in Batman's origin would make him the perfect arch-nemesis for Batman. Furthering this connection, they take him to the old theater where Bruce's parents were murdered. There they set up an army of Jokers to delay Batman, Batgirl, and Red Hood as they rush to stop the birth of a new Joker.
Barbara and Jason fend off the legion of Jokers so Batman can face one of the original Jokers. This Joker holds Chill over the same vat of chemicals that turned him into DC's darkest criminal mastermind. On the big screen, Joe confesses to killing Martha and Thomas Wayne on that fateful night, but more importantly, he apologizes for his actions. Whether this inspires Bruce or not, he still makes an effort to save the man who ruined his life. The Joker laughs and tells Batman that Joe will find humor in the death of Bruce's parents once he turns into a Joker. There's just one flaw in the Joker's plan... Joe Chill literally has weeks to live. When Batman brings this up, the Joker says that the vat of chemicals will cure Joe's body but ruin his mind. In classic Batman fashion, Batman beats the Joker and saves Joe. In a moment of catharsis, Bruce sits by Joe in his final moments, having finally moved past the trauma that made him Batman.
Somehow, in a series featuring a jokerized shark, this remains the wildest element. While some readers might wonder how truthful the Joker is being when he claims the vat of chemicals will cure Joe, Batman doesn't comment on the subject further than the initial point and it doesn't come across like the Joker is lying. The dramatic implication of the scene is that the Joker is right.
While this could have wide-reaching implications on the DC Universe, this is obviously a plot convenience. Ironically enough, there was a storyline in 2001 titled The Joker's Last Laugh that was about the Joker having a brain tumor and going on one last crime spree. Conveniently it is later revealed that he never had a tumor at all, so it wasn't like the chemicals helped him with the situation. Regardless of whether the chemicals actually do cure cancer or not, Batman: Three Jokers #3 is a perfect example of how minor plot conveniences can leave readers with more questions than comic creators intend.