Probably Harry Potter and Edward Cullen. Since Edward is sort of the main character among the Cullens in a way, and Harry is the central figure in his world. They both have unique abilities and a sense of responsibility, so it makes sense for them to be the first to cross paths and start interacting.
Another likely pair could be Ron and Emmett. Ron is a bit of a joker and Emmett seems like the type who would enjoy some light - hearted banter. Ron might be initially scared of Emmett's vampire strength but then realize that he's actually a friendly (for a vampire) guy. And Emmett would find Ron's clumsy yet endearing ways quite amusing.
It could be Hermione and Alice. Hermione is very inquisitive and intelligent, and Alice has the ability to see the future. Hermione would be really interested in Alice's power and might start asking her all sorts of questions. Alice, on the other hand, would be curious about Hermione's knowledge of magic and her no - nonsense attitude.
Definitely Harry Potter and Finn Hudson. Harry is the hero in the wizarding world, and Finn is a key figure in the Glee club. They could bond over their leadership roles. Harry could teach Finn some magic tricks, and Finn could show Harry how to be more confident while performing in front of a large audience.
Most likely, it would be Harry Potter and Nico di Angelo. Harry is the main character in his world and is always the one to step forward when something strange is going on. Nico, being the son of Hades, has a certain air of mystery around him. So, when he appears in the wizarding world, Harry would be the one to approach him out of curiosity and a sense of duty to protect Hogwarts from any potential threat.
Probably Ash and Iron Man. Iron Man is always curious about new things and Ash with his Pokémon would be quite an interesting sight for him. He'd likely approach Ash first to ask questions about what he is and what those strange creatures are.
It could be Percy and Black Widow. Natasha is a master of reading people, and she'd notice Percy right away. She might approach him in a more stealthy way compared to the others, trying to assess if he's a threat or an ally. And Percy, being used to danger, would be on his guard at first, but then start to trust her as she shows her good intentions.
Hermione and Betty would be likely to interact. Hermione's intelligence and thirst for knowledge could pair well with Betty's investigative nature. They could work together to solve a mystery that spans both the wizarding world and Riverdale.
Applejack and the Heavy might be the first to interact. Applejack is a hard - working and practical character. The Heavy is a no - nonsense fighter. Applejack might see the Heavy and be curious about his large size and strange weapon. The Heavy, on the other hand, might be interested in Applejack's farming skills and the fresh apples she might be carrying. Their down - to - earth personalities could lead to an initial interaction.
Obviously, Harry Potter himself would be a main character. He is the central figure in the Harry Potter series. Then, from the Cullen family, Edward Cullen would likely be a main character. He is the most prominent of the Cullens in the Twilight series and his abilities and personality would make for an interesting interaction with Harry.
Harry Potter himself could interact with Sophie from Huntik. Harry is used to facing great challenges and having a strong sense of justice. Sophie, with her connection to the Titans, could find common ground with Harry in their fight against evil. They could learn from each other's worlds and work together to overcome a powerful dark force that threatens both universes.
Obviously, Harry Potter himself is very likely to interact with the Beast King. He has a natural inclination towards helping those in need and has a great sense of justice. Hermione Granger would also be a great character to interact with the Beast King. With her vast knowledge of magic and books, she could offer valuable insights about the Beast King's powers and history.
Harry Potter himself is a likely candidate. Given his heroic nature and penchant for getting involved in dangerous situations, he might be the one to first encounter Starscream. His experience with facing dark wizards could give him some skills to deal with the unpredictable Starscream.