One idea could be a crossover with the Harry Potter universe. The Avengers could travel to Hogwarts in search of a magical relic that could help them in the fight against Thanos. Maybe Doctor Strange uses his magic to open a portal to Hogwarts and they team up with the wizards to defend the relic from Thanos' minions.
Another plot could involve a crossover with the DC universe. Superman and the Avengers join forces against Thanos. There could be some interesting character interactions, like Iron Man and Batman comparing their gadgets, or Thor and Superman having a friendly competition over who is stronger. And they all have to figure out how to combine their different powers and strategies to defeat Thanos.
One idea could be exploring how the remaining heroes deal with the loss of half the population on a personal level. For example, Iron Man could struggle with survivor's guilt and pour all his energy into finding a way to reverse it. Another could be about the new friendships formed among the survivors as they realize they have to rely on each other more than ever.
One idea could be exploring the backstories of the minor characters in more depth. For example, showing how the Wakandan warriors trained and what their lives were like before the big battle. Another could be a what - if scenario where Thanos actually had a change of heart at the last minute. Maybe he saw the beauty in the universe he was about to destroy and decided to stop.
A possible plot could be that Deadpool somehow gets his hands on one of the Infinity Stones before Thanos does. This attracts the attention of Thanos, who then sends his minions after Deadpool. Spider - Man has to protect Deadpool while they try to figure out what to do with the Stone. This leads to a series of wild adventures and battles, with the two heroes learning more about each other and growing as characters.
One idea could be that Spider - Man discovers a hidden power within himself during Infinity War that allows him to turn the tide of the battle. Maybe he can communicate with the Infinity Stones on a deeper level, using his spider - sense to detect their weaknesses and strengths.
One idea could be Superman teaming up with the Avengers in a way that defies the normal rules of their universes. Maybe he has a unique power that helps them against Thanos, like his super - breath freezing Thanos' army.
One idea could be creating an OC (original character) who is a powerful mage from a hidden dimension. They could have unique powers that disrupt Thanos' plans in unexpected ways. For example, their magic could nullify the power of the Infinity Stones temporarily.
One idea could be that Spider - Man discovers a hidden power within himself during the Infinity War. Maybe he has a unique connection to the Infinity Stones that no one else realizes. This power could help him turn the tide in some crucial battles.
One idea could be to have the cartoon versions of the heroes and villains swap powers. For example, Iron Man could end up with Thor's lightning powers and Loki could have access to Captain America's super - soldier strength. This would lead to really unique battles and character development as they struggle to control new abilities.
One idea could be exploring the family dynamics within the Avengers during the Infinity War. For example, how do the different characters who have a sort of family bond, like Tony Stark and Peter Parker, deal with the chaos of the war? Another could be a fanfiction where a superfamily from a different dimension arrives to help in the Infinity War and how they interact with the existing heroes.
One idea could be exploring what would happen if a minor character from the movie got the Infinity Stones instead of Thanos. For example, a random Asgardian soldier who survives the initial attack on the ship. They might use the Stones in a completely different way, perhaps to restore Asgard rather than wipe out half of the universe.