Some characters might have to form alliances with certain underworld entities. Neville, for example, could befriend a minor underworld deity who is sympathetic to their cause. This deity could then help them understand the complex power structures in the underworld and guide them through dangerous areas. In return, the characters could offer the deity something unique from the wizarding world, like a rare potion ingredient.
Interaction could also be based on challenges. The underworld entities might set up magical challenges for the Harry Potter characters. If they succeed, they get what they want, like information or passage through a particular area. Ginny, being a brave character, could take on these challenges head - on, using her quick thinking and her skills in defensive magic to overcome them.
They can interact through magical means. For instance, Harry could use a translation spell to communicate with underworld spirits. The characters might also use magical objects as a form of currency or bargaining chip. Like, a powerful wizarding wand could be highly sought - after in the underworld.
I think Michael Corvin could be an interesting crossover character. He's a hybrid in the Underworld series, which means he has a unique set of abilities. In the Harry Potter world, he could be seen as a strange new kind of magical being. He might be able to help the wizards understand different types of magic that are more physical and instinct - based like his own. Also, his journey of self - discovery in the Underworld could be paralleled in the wizarding world as he tries to find his place among the wizards and witches.
One idea could be that the characters from the Underworld series find their way into the wizarding world. For example, Selene could end up at Hogwarts. Maybe she's on a hunt for a new type of vampire that has taken refuge among the students. The wizards would be both intrigued and a bit scared of her skills and her lycan - slaying abilities. Another idea is that the magic from the Harry Potter world could be used to try and solve some of the problems in the Underworld, like the eternal war between vampires and lycans. What if Dumbledore tried to broker peace between the two factions using his wisdom and powerful magic?
In a crossover, the underworld could have its own form of magic that is different from the magic in the wizarding world. Ron could be the one to first discover a connection between the two magics. He might find an old artifact in the wizarding world that has a link to the underworld. This could lead to an adventure where the trio explores the underworld to prevent a dark magic from the underworld from spreading into the wizarding world.
Another way of interaction could be through magical artifacts. Let's say there is an ancient artifact in the Harry Potter world that is a link to the Magic God. The characters might discover this artifact and accidentally or purposefully activate it. This would then draw the attention of the Magic God, and it could start to influence the events in the wizarding world, interacting with the characters through the power of the artifact.
Another way it could work is through a character's quest. Let's say a character in the Harry Potter world is searching for a way to defeat a new kind of dark magic that has some similarities to the dark forces in Selene's world. They travel to find Selene, and together they combine their knowledge and skills. Selene's knowledge of the underworld's dark secrets and Harry's understanding of magic could create a unique way to fight this new threat.
The characters would likely be initially cautious. For example, Hermione might be skeptical about the dragon - based magic in Eragon's world. She would want to study it first. Harry, on the other hand, might be more open - minded and eager to learn about Eragon's bond with his dragon. Eragon would probably be curious about the wands and the organized system of magic at Hogwarts.
Harry Potter would likely be very curious about Superman. He might ask him a million questions about his powers and his world. Superman, on the other hand, would be intrigued by the magic that Harry and his friends possess. Hermione would probably try to study Superman scientifically at first, but then be amazed by his abilities that seem to defy science.
Harry and Moana would likely become fast friends. Harry would be intrigued by Moana's courage and determination, while Moana would be fascinated by Harry's magic. They would share their stories and learn from each other.
Well, Thor is a very confident and powerful character. He might be initially a bit baffled by the wizards and witches at Hogwarts. Harry, on the other hand, would be in awe of Thor's strength and abilities. Thor could probably teach Harry some physical combat skills, while Harry could introduce Thor to the subtleties of wizard magic like apparition.
The characters could interact in some really interesting ways. For example, Maleficent's presence in Hogwarts could cause chaos among the students. Some might be in awe of her, while others would be terrified. Harry would probably try to reason with her, using his own experiences with the dark side. Hermione might offer to help her with her magic if she thought it could lead to a positive outcome. And Ron would be there, providing some comic relief with his clumsy attempts to deal with the situation. There could also be some great duels between Maleficent and the Hogwarts professors as they try to keep the school safe from her unpredictable actions.