What I would change:
1. Remove Jeremiah entirely, only have Jerome. He was more charismatic and deliciously evil. But I would incorporate some stuff from Jeremiah's story too which I found interesting.
2. Have Jerome's past more mysterious:
- Have Jerome drop comments on how he was abused by his family, but everyone else would claim that Jerome wasn't innocent either: for example he played pranks on other circus kids which nearly resulted in them suffering critical injuries (like pushing them into bear traps)
- Maybe the family tried to give Jerome to foster parents not wanting to do anything with him, however Jerome proved too problematic even for them. This could lead to Jerome being in various schools and somewhat educated, while at the same time Jerome would educate himself as well by often going into libraries and reading.
3. During his first appearance, he tries to frame one of his mother's lovers for the murder which almost succeeds if it weren't for Cicero's change of heart during the last minute. After he gets caught I would keep Jerome off-screen for a while. He would appear for one episode during which Bruce and his class has a trip to Arkham Asylum, each student has to talk with an inmate using fake names. Jerome gets to meet with Bruce for the first time and have a talk about human nature, with Bruce believing that anyone can be good while Jerome believes that everyone is doomed to become vile as he is. The talk ends with Jerome recognizing Bruce from the papers and telling how he had a good chuckle over the deaths of his parents which causes Bruce to nearly lose his cool before he gets taken away. This begins the twisted obsession that Jerome will have with Bruce.
4. He escapes Arkham Asylum on his own by sneaking out. He joins the Galavans and acts as a personal enforcer and hitman for them for a while. However, eventually he feels that the Galavans are too controlling for him so he decides to f*ck them over by using some avarage joe to blackmail them. At the same time, Jerome overhears a drunk Theo Galavan trying to make an idea on how to become a mayor. Jerome then begins to manipulate Theo into breaking out some of the most dangerous inmates of Arkham Asylum and create the Maniax. Jerome is completely in charge of the Maniax's actions, like setting the bus full of cheerleaders on fire (in this version they succeed) and the other horrible stuff they do. The Maniax cult begins to emerge, while Theo tries to orchestrate the Gala events, Jerome has other plans: behind-the-scenes he works along with the Maniax cult to betray Galavan and cause more chaos throughout Gotham.
5. During the Gala, almost everything goes on as it does in the show, however Jerome kills Theo and kidnaps Bruce with his followers, intending to kill Bruce because Jerome was annoyed by him and to reunite him with his family in a twisted way. They wreak havoc in the city untill Azrael jumps in and kills Jerome. Jerome dies thinking that it was Galavan, however in reality it was Tabitha in disguise. Jerome's right hand man, Dwight takes over the cult and begins his plan to sabotage Hugo Strange's Indian Hill project and resurrect Jerome.
6. Jerome's resurrection story arc is exactly the same as it was in the actual show.
7. After Jerome gets incarcerated in Arkham, he begins to deeply think about Bruce as he found a new sense of fondness for Bruce's rage in the House of Mirrors and their clashing ideologies. Jerome realizes that they aren't too different as their paths were caused by traumas caused by events connected to their families. Jerome begins to have a new plan to break Bruce and mold him into some sort of brother-like figure he never had.
8. Jerome, Mad Hatter, Penguin and Scarecrow escape Arkham and form the Legion of Horribles. Almost everything goes down the same way as it does, except Jerome recruits Zsasz and Riddler as well. Jerome is aware that Riddler and Penguin are planning to usurp him, however Jerome knowing of their past begins to manipulate both, turning them against each-other. During the concert episode, Jerome tries bring out the hidden insanity withing Bruce on stage giving him the knife to kill Jerome (kind of how he did it with Jeremiah). Bruce refuses to do so, which only ends in Jerome beating him up on stage. Before Gordon could try to kill Jerome, he escapes.
9. Gordon and Bruce begin to have conflict over whether Jerome deserves some form of redemption or not. This results in both of their attempts to stop Jerome to fail.
10. No Man's Land doesn't really happen, but Gotham would become a near-irrepairable sh*thole thanks to Jerome and the Horribles. Jerome does the "Ace Chemicals" plot with Bruce which lead to them fighting in Ace Chemicals. Then we would get a scene similar to the actual 4x18 with Bruce and Jerome. The former offers to help and rehabilitate Jerome, however the clown refuses and claims that their war against each-other will continue and thus Jerome allows himself to fall into the acid completing his transformation into the Joker. Bruce fearing that Jerome’s words are true, leaves Gotham for 15 years to become the city's true protector against Jerome and the other villains.
11. Fifteen year time jump happens, with Joker being in Arkham secretly plotting a "welcome home party" for Bruce. Bruce returns as Batman, and after revealing that he has been faking amnesia and his catatonic state for 15 years, he enacts revenge on Riddler and Victor Zsasz (because they made fun of him during these years) by putting them through psychologically torture in shock therapy, this later caused both Riddler and Zsasz in becoming much more evil and insane versions of themselves (Zsasz becomes the serial killer from the comics and Riddler becomes similar to his Reeseverse version). He attempts to unleash deadly chemicals upon Gotham to destroy the city further. He attempt to destroy everything connected to the Wayne Family as a "welcome home gift" for Bruce Wayne and attempts to disfigure Jim Gordon's and Lee Thompkins' daughter by dropping her in a pot of boiling chemicals. Batman saves the day and Joker gets back into Arkham.
