For a Stranger Things crossover fanfic, consider a crossover with the Lord of the Rings. The Upside Down could be like Mordor, and the characters from Stranger Things could play a role in the fight against Sauron. It would be interesting to see how Eleven's powers would compare to the magic in Middle - earth. Another idea is a crossover with the Matrix. The kids might discover that the Upside Down is part of a computer - generated simulation like the Matrix. And a crossover with the Teenage Mutant Ninja Turtles. The turtles could come to Hawkins and fight the Demogorgon side by side with the kids.
A Stranger Things crossover fanfic with the Avengers would be really exciting. The Hawkins kids could team up with the Avengers to fight off the Demogorgon which has somehow become a threat to the entire world. Or a crossover with Doctor Who. The Doctor could land in Hawkins and help the gang deal with the Upside Down, bringing his unique time - traveling and alien - fighting skills. Also, a crossover with the Ghostbusters would be fun. They could come to Hawkins to deal with the strange entities from the Upside Down using their proton packs.
Another great concept is a crossover where Eleven's powers are mistaken for some kind of witchcraft by the Supernatural universe. Sam and Dean initially think she's a threat but then realize she's actually a powerful ally against a common enemy. They could be facing a powerful being that can manipulate time and space, and Eleven's telekinetic and telepathic abilities are crucial in defeating it.
Another idea is a crossover of the Upside Down and the Weirdness of Gravity Falls. Imagine Eleven using her powers in Gravity Falls and discovering new and strange things about the town. The kids might explore areas where the laws of physics seem to be a mix of both their worlds. For example, they could find a portal that leads to a place that has elements of both Hawkins and Gravity Falls.
One great Stranger Things crossover fanfiction is the one that combines it with 'Harry Potter'. It imagines the characters from Stranger Things attending Hogwarts. The way the Upside Down is incorporated into the magical world is really interesting. It adds a new layer of mystery and danger.
In Stranger Things crossover fanfics, Dustin is quite popular. His intelligence and his love for science can lead to interesting interactions in crossovers, for example, in a crossover with a scientific - based fictional world. Max Mayfield is also a favorite. Her skateboarding skills and feisty personality can add a lot to crossovers. And then there's Will Byers. His connection to the Upside Down can be explored in many different crossovers, such as in a crossover with a horror - themed universe.
One great 'Stranger Things 4 Fanfic' is 'The Upside - Down Revisited'. It delves deeper into the Upside Down and how the characters interact with the new threats there. It has really good character development, especially for Eleven. Another one is 'Hawkins' New Horrors' which focuses on the town's reaction to the events of season 4 and how the community bands together or falls apart. There's also 'Beyond the Gate', which explores what might be on the other side of the gates that keep opening up in Hawkins.
There's also 'Byers Brothers' Adventure'. This fanfic follows Will and Jonathan Byers on a side adventure that wasn't shown in the show. It has great character development and a really engaging plot.
Perhaps a story where Steve and Robin get involved in a time - travel adventure within the Stranger Things universe. They accidentally stumble upon a portal that sends them back in time, and they have to find their way back while also changing some small but significant events in the past.
One idea could be that the Demogorgon from Stranger Things somehow ends up in Derry from It. The Losers' Club and the kids from Hawkins could team up to fight it. They would have to combine their different skills and knowledge of the supernatural.
One idea could be that the Losers' Club from 'It' somehow ends up in Hawkins, Indiana, during the events of 'Stranger Things'. They could team up with the kids from 'Stranger Things' to fight a new, combined threat that has elements of both the Upside Down monsters and Pennywise's terrors. For example, the Mind Flayer could merge with Pennywise in some way, creating an even more terrifying entity.
I would recommend 'Hawkins' Hidden Love'. This fanfic delves deep into the lives of the Stranger Things characters in a gay context. The author does a wonderful job of creating a believable story line. It has a great balance between the mystery and drama elements that are so characteristic of Stranger Things, and the exploration of the gay relationships among the characters. It's definitely worth checking out.