Well, Ron might be initially terrified of Slenderman. But when his friends are in danger, he would step up. The Weasley twins could try to play pranks on Slenderman, not fully realizing the danger at first. Dumbledore, on the other hand, would be very cautious. He might observe Slenderman from a distance, trying to understand his nature before taking any action. In a 'Harry Potter and Slenderman fanfic', these interactions would create a lot of interesting scenarios.
In a fanfic, Hagrid could be one of the first to encounter Slenderman in the Forbidden Forest. Hagrid's knowledge of strange creatures might make him think he can handle Slenderman, but he quickly realizes this is a different kind of threat. Meanwhile, the students at Hogwarts might start having nightmares about Slenderman, and Harry and his friends have to figure out a way to stop these nightmares and deal with Slenderman. Neville could also play a role, perhaps using his knowledge of plants to try and create some sort of defense against Slenderman.
Well, in a Harry Potter fanfic involving Mummy Holmes, perhaps Mummy Holmes could be a mysterious figure at Hogwarts. She might use her detective - like skills to solve some of the strange mysteries that occur within the school. For example, if there are some strange disappearances or unexplained magical happenings, she could be the one to piece together the clues.
Carmen could be a mysterious visitor to Hogwarts. Harry Potter, being the curious and brave wizard he is, might be intrigued by her and try to figure out her motives. Waldo, being always lost, could accidentally end up at Hogwarts through some magical portal. Carmen might use her skills to help Waldo find his way back home while Harry Potter helps them avoid getting caught by the Hogwarts faculty who might be suspicious of their presence.
Harry could teach Red Riding Hood some basic spells. For example, he could show her how to use the Lumos charm so she can see better in the dark forests.
The characters would interact in very strange ways. The Hogwarts students would be shocked by the Jackass crew's behavior. The Gryffindors might be initially intrigued, while the Slytherins would be disdainful. Harry and his friends would probably try to keep the Jackass guys out of trouble, but it would be difficult as they are always looking for the next wild thing to do.
Harry might be in awe of Elsa's powers at first. He would likely approach her with caution and respect, as he does with most powerful beings. Elsa, on the other hand, would be curious about Harry's world of wands and spells. They could start by sharing their stories. Harry would talk about Voldemort and his battles, and Elsa would share her experiences with her frozen kingdom and her isolation.
The Stargate characters are used to dealing with advanced technology and alien cultures. When they meet the Harry Potter characters, they might be initially confused by magic. For example, Jack O'Neill might be both amused and intrigued by the spells the wizards cast. Meanwhile, Harry Potter and his friends would be curious about the Stargate technology and the different worlds it can access.
The Avengers could be impressed by the magic of the Harry Potter characters. For instance, Captain America might be in awe of the Patronus charm. And the Harry Potter characters could be amazed by the Avengers' superpowers. Hermione might be very interested in Bruce Banner's scientific knowledge.
She might interact with Hermione in a way that challenges Hermione's logical view of relationships. Aphrodite could introduce her to a more emotional and instinctive side of love. They could have conversations about how love is not always something that can be explained by books or logic, and this could lead to Hermione having a different perspective on her own feelings for Ron or other potential partners.
Android 18 could be a protector for Harry. Given her strength, she could easily fend off Death Eaters. Harry, in turn, could introduce her to the magical world, showing her spells and potions. For example, she might be amazed by the invisibility cloak and they could use it for some strategic advantage.
Hermione could study the Kubikiribocho. She would pour over books in the Hogwarts library to figure out its origin and powers. Harry, on the other hand, might be the one to actually pick it up and test its abilities in combat. Ron could be a bit skeptical at first but would come around when he sees the sword's potential against the dark forces. For example, the sword might react differently to different spells cast at it. Harry could learn to use these reactions to his advantage in battles.