A villain could be a corrupted version of a well - known Spider - Person. Maybe in one universe, a Spider - Person succumbs to the power they have and becomes a power - hungry tyrant who wants to control all the other Spider - Verses. They use their knowledge of the multiverse and their powers to create chaos and try to take over.
One idea could be exploring a different Spider - Person's origin story within the multiverse. For example, a Spider - Person from a world where spiders are sentient and work together with the human Spider - Person. Another could be a story where all the Spider - People have to team up against a villain who can manipulate time across the multiverse, causing chaos and disrupting the fabric of each Spider - Verse.
One great 'Across the Spider - Verse Fanfic' is 'Spider - Verse Bonds'. It focuses on the relationships between different Spider - People. It shows how they interact, support each other, and grow together in this multiverse. It has really engaging character development.
First, know the source material well. Understand the characters, their powers, and the multiverse concept in 'Across the Spider - Verse'. Then, come up with an original idea. It could be a new villain, a different relationship dynamic, or a unique adventure. For example, you could write about a Spider - Person from a dimension we haven't seen yet.
In many aspects, 'Across the Spider-Verse' adheres to the comic book canon. However, there might be some creative liberties taken to make the story more cinematic and engaging for the audience while still respecting the core elements of the comics.