Gandalf would be really interesting. He could interact with Dumbledore and they could exchange their knowledge of magic and wisdom. They are both powerful and respected figures in their respective worlds. Gandalf could also teach the Hogwarts students about different forms of magic that are more nature - based like his own.
Legolas would be a great addition. His archery skills combined with the magic of the 'Harry Potter' world could create some exciting scenarios. For instance, he could be invited to Hogwarts to teach a special class on combat skills, and the students would be in awe of his abilities. He could also help in battles against dark forces in the 'Harry Potter' world, using his speed and accuracy.
I think Frodo would be an interesting character to add. His journey to destroy the One Ring is full of challenges and moral dilemmas. In the 'Harry Potter' world, he could be a symbol of hope and perseverance. He could share his experiences with Harry and his friends, and perhaps inspire them to face their own challenges in a different way. Also, the idea of how the magic in the 'Harry Potter' world would interact with the power of the One Ring could be explored.
Harry Potter himself would be very interesting. Combining his wizarding skills with Kryptonian powers would make him an extremely powerful character. He could be the bridge between the two worlds and use his new powers to protect both the wizarding world and the world of Kryptonians on Earth.
A fanfiction could explore what would happen if Voldemort somehow made an alliance with Sauron. This would create a huge power struggle and force the heroes from both worlds to join forces in a more complex way. The wizards from Hogwarts would have to learn to fight in a very different kind of battle, and the Middle - earth characters would be both amazed and wary of magic.
Hermione would be really interesting. She could bring her intelligence and knowledge of magic to the iCarly crew. Imagine her helping Freddie with his tech projects using magic, or teaching Carly and Sam some basic spells. It would be a great contrast between the magical and Muggle worlds.
Harry and Elsa would be a very interesting pairing. Harry, with his experience in facing dark magic, could offer Elsa a new perspective on her powers which she has always seen as a curse. And Elsa, with her ice powers, could show Harry a different kind of magic that he's not used to in the wizarding world. Another interesting pairing would be Ron and Kristoff. They both have a simple - minded charm and could get into all sorts of funny situations together, like getting lost in the Forbidden Forest or on the mountains in Arendelle. Also, Hermione and Anna would be great. Hermione's intelligence and Anna's determination would make them a formidable duo as they try to solve problems in both their worlds.
Snape and Madarao would be an unexpected but fascinating pairing. Snape's brooding and complex personality could interact in an interesting way with Madarao's more straightforward and loyal nature. Snape could perhaps study the unique yokai magic associated with Madarao, and Madarao could be both amused and intrigued by Snape's potions and spells.
Definitely Harry Potter and Rias. Rias is used to leading and being in control, but Harry has his own strong sense of justice and leadership. Their interactions could be full of power plays and mutual respect as they try to figure out how to work together.
It could be Aquaman. He is so different from the wizards in the Harry Potter universe. His fish - like abilities and his role as a king would make for some great interactions with the Hogwarts students and professors. He could teach them about the ocean and its secrets, while also being amazed by the magic of wands and potions.
Percy would be really interesting. His ability to control water and his laid - back yet brave personality would contrast well with the more formal wizarding world. He could make some really funny and unexpected interactions with the Hogwarts students and teachers.
I think Hermione would be really interesting. She's already very intelligent and resourceful. If she got the Venom symbiote, she could use its powers to access areas that are normally restricted in the wizarding world, like the restricted section of the library, and find new spells and knowledge. She could also use the symbiote's physical abilities to protect her friends during dangerous situations.
I think Harry Potter and Nick Burkhardt would be an interesting pairing. Harry has his experience with fighting dark magic and Nick has his knowledge of the Wesen world. They could learn a lot from each other. Harry could teach Nick about some of the more complex spells, while Nick could introduce Harry to the different types of Wesen and how to deal with them.