A great 'Harry Potter' underworld don fanfiction might explore the idea of the don being a Muggle - born who was shunned by the wizarding world and thus turned to the underworld. But he still has a good heart and uses his underworld influence to help Harry and his friends. He could provide them with safe houses in the Muggle world that are magically protected, using a combination of his Muggle knowledge and the little magic he has learned on his own.
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.
Many Harry Potter underworld fanfiction also have a theme of redemption. A character who has been involved in the underworld may try to find a way to break free from it and redeem themselves. It adds an interesting layer of depth to the story, showing that not all who are in the underworld are completely lost.
Another way is to join 'Harry Potter' fanfiction groups on social media platforms. Ask the members if they know of any good fanfictions with an underworld don in the 'Harry Potter' universe. They might be able to recommend some great reads based on their own experiences.
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.
One idea could be that Selene finds herself magically transported to the wizarding world of Harry Potter. She might initially be confused but then use her skills as a vampire to help in some sort of battle against dark wizards. For example, her enhanced speed and strength could give the Order of the Phoenix an edge in a fight.
Maybe through a series of unexpected magical events. For instance, he could accidentally stumble upon a powerful ancient magic in the Forbidden Forest that has a connection to the underworld. This magic could bind him to the underworld in a way that gives him the position of king. Or perhaps he is tricked by a dark wizard who wants to get rid of him by sending him to the underworld, but instead, he ends up ruling it due to his natural leadership skills and the respect he gains from the underworld creatures.
Sure. Some fanfiction might focus on an elder vampire character who has a long history and how they might view the events in the Harry Potter world. They could be a neutral party, or perhaps they have their own motives for getting involved. Another aspect could be the underworld aspect. It could be a hidden part of the wizarding world that is rarely explored in the original series, filled with all sorts of dark and mysterious creatures, and in fanfiction, it could be expanded upon with vampires being a major part of that underworld society.
There's also 'Into the Harry Potter Underworld'. This one starts with a young wizard accidentally stumbling upon an entrance to the underworld. As he ventures deeper, he discovers dark magic practices and a whole new world of power struggles. The author does a great job of building tension throughout the story.
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?