In a fanfiction, the Joker could also develop by forming an unlikely alliance. He could team up with a hero or an anti - hero, not out of good intentions but for his own self - serving reasons. This alliance could change his perspective on things and how he approaches his evil plans, thus developing his character in a new way.
One interesting plot idea could be a fanfiction where the Joker somehow comes back to life in Arkham Knight. Maybe he was only in a coma and wakes up with a new, even more deranged plan to take over Gotham. He could start by manipulating the inmates in Arkham again, creating chaos from within the asylum.
Probably. The Arkham series has a connected storyline, and it would make sense for the Arkham Knight new story to be a continuation. This way, it can keep the lore consistent and develop the characters further. For example, we might see how Batman has changed since the last encounter with his foes.
The Arkham Knight's origin story is quite complex. He was created as a military-trained antagonist to Batman. He has a vendetta against Batman, partly due to his own past experiences and the events that led him to become this highly skilled and vengeful figure. He was trained in combat and strategy, making him a formidable foe for Batman in the Arkham series.
Yes, there are many Arkham Knight fanfics that are suitable for general audiences. You can find them on various fanfic websites by using filters or search terms like 'family - friendly Arkham Knight fanfic' or 'PG Arkham Knight fanfic'.