Severus Snape is also a popular choice. His complex character and vast knowledge of magic can create interesting dynamics when he meets characters from different magical worlds. He could either be a mentor or an antagonist in these crossovers.
Another idea could be Harry learning magic from a time - traveling wizard from a far - off future. This would introduce futuristic magical concepts and technologies that he would have to adapt to. It could also lead to him having to use his traditional Hogwarts magic in new and unexpected ways to keep up with the advanced magic he's learning.
A very common one is Sherlock Holmes. Imagine Harry being raised by the brilliant detective. He would grow up with a sharp mind for deduction, which could be very useful in solving the mysteries within the wizarding world. Another is Gandalf from 'The Lord of the Rings'. Gandalf could teach Harry a different kind of magic and wisdom, which would shape Harry into a very different kind of wizard.
Often, Harry Potter himself is a central character. He might interact with immortals and be influenced by their ways. Hermione could also be there, using her intelligence to understand the immortals and their magic. Voldemort could be another common character, and his quest for power might be affected by the presence of immortals. Maybe he tries to gain immortality from them or is in conflict with them because they pose a threat to his plans.
In many 'harry potter horror crossover fanfiction', Sirius Black can be a key character. His time in Azkaban and his connection to the dark arts (through his family) can be used to create horror - inspired storylines. Luna Lovegood might also be included as she has an open - minded and somewhat otherworldly view. This could lead to her being the first to sense the encroaching horror elements in the wizarding world, like strange new creatures or dark magic manifestations.
In a Harry Potter and LOTR crossover fanfiction, black magic could take on different forms. In the Harry Potter universe, it's often associated with the Dark Arts like the Unforgivable Curses. In LOTR, dark magic is related to Sauron and his minions. A crossover might explore how wizards from Harry Potter's world react to the more ancient and malevolent black magic of Middle - earth.
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.
One common theme is self - discovery. As Harry learns light magic, he often discovers new aspects of himself and his potential. Another theme is the power of good over evil. Light magic is usually depicted as a force for good, so it's about using it to combat the dark forces in the wizarding world.
Edward Cullen and Harry Potter are often popular. The contrast between Edward's vampire nature and Harry's wizardry makes for an interesting dynamic. Fans like to imagine how they would react to each other's powers and the situations they face.
Obviously, Harry Potter is a main character as the title suggests. He is the one who is on the journey of learning wandless magic. Hermione Granger could also be an important character. She might be helping Harry research about wandless magic, using her vast knowledge from the library.
Some concepts include crossovers with fairy tale worlds. Picture Harry Potter characters entering the world of Cinderella or Snow White. The magic in Harry Potter could transform the classic fairy tale settings. Another concept is a crossover with steampunk elements. In such fanfiction, you'd see magic integrated with steam - powered machinery and Victorian - era aesthetics. This could lead to the creation of new magical devices and a whole new look at how magic is used in a more industrialized setting. There could also be crossovers with alien races, where the wizards' magic is put to the test against extraterrestrial powers and technologies.