How about Gollum from Lord of the Rings? It seems really odd at first, but think about it. Gollum's sneaky nature and knowledge of dark places could be useful in Arkham Asylum. Batman could try to control Gollum's greed and use his skills to navigate the more dangerous parts of the asylum. And Gollum might be fascinated by Batman's shiny gadgets. It would be a very strange and interesting dynamic.
I think Gizmo from the Teen Titans could be really unexpected. He's used to dealing with high - tech and more colorful villains. Throwing him into Arkham Asylum, with all its dark and gritty atmosphere and dangerous inmates, would create a really interesting dynamic. He could try to use his gadgets to either escape or try to take over the asylum, which would be hilarious considering the much more menacing villains there.
Another plot could involve a crossover with a fantasy world. Imagine Batman being transported to a world like Middle - earth. He'd have to use his gadgets and combat skills in a world full of magic and mythical creatures. He might team up with characters like Aragorn or Legolas to fight against an evil force that has some similarities to the criminals in Arkham Asylum, perhaps a dark sorcerer who is as mad and unpredictable as the Joker.
Brainiac could also work well. He is an android with an insatiable thirst for knowledge and a penchant for collecting and destroying planets. In a crossover, he could target Earth, specifically Gotham and Metropolis. His advanced technology would pose a major challenge to both Superman and Batman. Superman's super - powers would be put to the test against Brainiac's powerful defenses, and Batman would need to use his wits to find a weakness in Brainiac's systems, leading to an exciting and complex story.
One common theme is the clash of different Arkham versions of characters. For example, when different interpretations of the Joker from various Arkham games meet. It creates interesting dynamics and often leads to intense showdowns.
One great 'Batman Arkham Asylum' fanfiction is 'The Dark Knight's Redemption'. It delves deeper into Batman's psyche as he battles his inner demons while trying to escape the asylum. The author does a great job of capturing the dark and gritty atmosphere of the game.
Cheetah could be a great villain. She has a connection to Wonder Woman already, but in a crossover, she could be working with some of Batman's rogues like the Penguin. The Penguin could provide the resources while Cheetah does the dirty work in combat against Batman and Wonder Woman.
One great Batman Arkham Origins crossover fanfiction is 'The Dark Knight's New Allies'. It combines elements from Arkham Origins with other DC universes. It has an interesting plot where Batman teams up with characters from different timelines. The story is well - written, with great character development.
The Powerpuff Girls. Blossom, Bubbles and Buttercup in the world of My Hero Academia would be amazing. They could team up with the female heroes like Uraraka and Tsuyu. Their superpowers could combine with the quirks in some really unique battles against powerful villains.
First, know the source material well. Understand the characters, the setting of Arkham Asylum, and the overall mood of the game. For example, Batman is a complex character with a dark past, so make sure to capture that in your writing.
A more complex fanfiction could involve all of Team RWBY in Arkham Asylum. Blake could use her stealth skills to move around unnoticed, Yang's strength would be useful in physical confrontations. They could be there because some powerful enemy has lured them there, thinking it's a place where they'll be weakened. But together with Batman and some of the inmates who might side with them (like Harley Quinn who has a complex sense of morality), they could turn the tables on the enemy.