The plot mainly revolves around Batman's encounters with Scarecrow. Scarecrow uses his fear toxins to spread chaos in Arkham. Batman has to face his own fears while trying to stop Scarecrow from causing more harm to the city.
For Scarecrow's character description, start with his physical presence. He moves in a jerky, almost inhuman way, like a puppet on strings. His hands are bony and claw - like. His eyes, which can be glimpsed through the holes in the sack, are filled with a manic glint. In terms of his character, he's obsessed with fear. He sees it as a tool, a weapon, and a form of art. He has no qualms about using it on anyone, whether they're a criminal or an innocent.
One idea could be exploring Scarecrow's backstory in more depth. Maybe show his early days in Arkham Asylum, how he was treated by the staff and inmates, and what led him to become the terrifying Scarecrow. Another plot could involve Scarecrow creating a new and more powerful fear toxin that not only affects Batman but also the citizens of Gotham, and Batman has to race against time to find an antidote while dealing with his own fears.
It enhances the series by adding more content. Simple as that. More stories mean more gameplay time and more things to discover about the Arkham world.
One possible aspect of a Batman and Harley fanfic in the Arkham universe could be their complex relationship. Batman is always trying to uphold justice, while Harley is often caught between her love for the Joker and her own sense of right and wrong. In a fanfic, the author might explore how Batman could potentially save Harley from her self - destructive path. For example, Batman could use his detective skills to show Harley the truth about the Joker's abuse towards her.
Definitely 'Batman: Year One'. Although Scarecrow doesn't have a huge role, his cameo and the implications of his existence in Gotham at that time are interesting. It sets the stage for future encounters. Also, 'Scarecrow: Year One' which focuses specifically on his origin story. It shows how he became the master of fear that he is in the Batman universe.
One of the best Scarecrow stories is 'The Long Halloween'. In it, Scarecrow adds to the overall sense of dread and mystery in Gotham. His fear toxin is used to great effect, making it a great read for Batman fans.
One of the best moments could be when Batman manages to outwit Harley in a battle of wits. He uses his knowledge of her psychology to predict her moves. For instance, if Harley tries to set a trap using her knowledge of Arkham's layout, Batman quickly figures it out and turns the tables on her.