One idea could be that the Demogorgon from Stranger Things somehow finds its way into the wizarding world of Harry Potter. The Hogwarts students, with their magic, have to figure out how to stop it. Another could be that Eleven has some latent wizarding abilities and she gets a letter from Hogwarts, then has to navigate both the Upside Down and the magical world.
One idea could be that the Demogorgon from Stranger Things somehow enters the wizarding world of Harry Potter. The students at Hogwarts have to use their magic to fight it. Another idea is that Eleven has some sort of magical connection to the wizarding world and she gets a letter from Hogwarts. Maybe she could learn magic there and use her powers in combination with spells.
One idea could be that the Demogorgon from Stranger Things somehow finds its way into the wizarding world of Harry Potter. The Hogwarts students would be both terrified and intrigued. They might initially try to use magic spells like Stupefy or Protego to fend it off. Hermione would probably be the first to start researching about this strange new creature, while Harry and Ron would be more on the front lines, trying to keep their classmates safe. The Stranger Things kids could also be magically transported to Hogwarts. Dustin would be amazed by all the magical creatures and would want to study them, Eleven might use her powers in new and unexpected ways in the wizarding world, like trying to communicate with magical portraits or using her telekinesis to move magic wands.
A cool plot could involve the Demogorgon from Stranger Things being somehow related to It. The Losers' Club and the kids from Stranger Things have to figure out this connection and stop both threats. The Losers' Club could share their knowledge of facing supernatural horrors with the Stranger Things kids, and vice versa. For example, Dustin's knowledge of science might help in understanding the nature of It, while Bill's leadership skills could inspire Mike Wheeler.
Well, in some fanfictions, Eleven could be sent to Hogwarts by mistake. Since she has telekinetic powers, the wizards might initially be very confused and intrigued by her abilities. She could form an unlikely friendship with Hermione, as both are very intelligent and resourceful. And then there's the idea of the Demogorgons being related to some dark magic creature from the Harry Potter universe, and the two sets of characters have to figure out how to defeat them together.
One idea could be that a character travels back in time to prevent the initial opening of the Upside Down. They could change a key event that led to all the chaos in Hawkins. For example, if they stop Eleven from using her powers in a certain way that originally weakened the barrier between dimensions.
One idea could be that the next generation discovers a new dimension that's even more dangerous than the Upside Down. They have to use the knowledge passed down from their parents, but also develop their own unique powers to deal with it.
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.
One idea could be a crossover where the ninjas from Naruto enter the Upside Down in Stranger Things. They use their jutsu to fight the strange creatures there. Another could be characters from Stranger Things learning chakra control in the Naruto universe. Maybe Eleven could use her powers in combination with Naruto's Rasengan.
One idea could be that Naruto characters are transported to the Upside Down in Stranger Things. They use their ninja skills to fight the strange creatures there. For example, Naruto could use his Rasengan against the Demogorgon.