It would probably be Harry Potter himself. He's from a world full of magic and mystery, and seeing him interact with the very real and regal world of the Queen would be fascinating.
Definitely Harry and Gaster. Harry is used to the magic in his world, while Gaster has his own set of abilities. Their meeting would be full of confusion, curiosity, and perhaps a bit of wariness. Another interesting interaction could be between Hermione and Gaster. Hermione would be eager to learn about Gaster's knowledge and would probably bombard him with questions.
It really depends on the situation. If they are in the wizarding world, Harry Potter would likely be more dominant as he knows the ins and outs of magic and the wizarding society. He can use spells to his advantage and has a deep understanding of the magical threats. But if they are in Oliver Queen's world, in Star City, Oliver would be more in control. He knows the city, has his team, and his combat skills are more useful in a non - magical urban environment.
Hermione Granger and Weiss Schnee could be a great pair. Hermione is highly intelligent and studious, while Weiss is refined and also has a great deal of knowledge. They could bond over their love for learning and perhaps work together on some sort of magical - mechanical hybrid project. For example, combining Hermione's magic knowledge with Weiss' understanding of Dust to create something entirely new.
Hermione Granger and Sherlock would be an interesting pair. Hermione is extremely intelligent and well - read in magic. Sherlock is a master of deduction. She could introduce him to the complex world of magic, and he could help her with his logical thinking when it comes to non - magical mysteries at Hogwarts. They could also have some really interesting debates about the nature of knowledge, whether it's through magic or pure logic.
I think Hermione would be really interesting too. She is so intelligent and knowledgeable about magic. When she meets Captain America, she would probably be very curious about his world and how things work without magic. She could be the one to try and find a way to bridge the gap between the two worlds, like trying to figure out how Muggle technology and magic could work together.
The interaction between Hermione and Carlisle would be really interesting. Hermione is super intelligent and always eager to learn, and Carlisle is a very old and knowledgeable vampire. They could have deep discussions about the nature of life, death, and immortality. Hermione might be fascinated by how Carlisle has managed to retain his humanity over the centuries, while Carlisle could be intrigued by Hermione's vast knowledge of magic and her strong moral compass.
I think Jack Frost would be the most interesting. He comes from a completely different world of ice and cold, and his powers are so different from the magic in the wizarding world. His carefree and mischievous nature would contrast well with the more rule - bound wizarding students at Hogwarts.
Hermione Granger and Spock would be really interesting. Hermione is known for her intelligence and knowledge. Spock is also highly intelligent and logical. They could have some really in - depth discussions about the differences between magic and science. Hermione could try to explain the principles of magic to Spock, and Spock could attempt to make Hermione understand the Vulcan way of thinking and the science behind the Enterprise's technology.
Definitely Harry and Wednesday. Harry is used to the rather normal, if magical, world of Hogwarts, while Wednesday is all about the dark and macabre. Their meeting would be full of contrasts. Harry's sense of right and wrong might be challenged by Wednesday's more amoral view of the world.
The interaction between Harry and Harley would be really interesting. Harry, with his sense of duty and moral compass, would be quite shocked by Harley's wild and unpredictable behavior at first. But as they get to know each other, they could learn from one another. Harry could teach Harley about loyalty and self - sacrifice, while Harley could show Harry how to be more spontaneous and not be so bound by rules.