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.
One more theme is the exploration of different cultures. The wizarding world in Harry Potter has its own unique culture, with things like Quidditch and the Houses. Middle - earth in LOTR has different races like hobbits, elves, and dwarves. In the crossovers, characters get to experience and learn about these different cultures. For instance, Hermione might be fascinated by the elvish language and lore, while Legolas could be intrigued by the spells at Hogwarts.
One idea could be that the One Ring somehow finds its way into the wizarding world. Maybe a Hogwarts student stumbles upon it during a field trip in an ancient forest. Another could be a wizard or witch from Harry Potter's world traveling to Middle - earth to study their different forms of magic. A third idea is that the characters from LOTR end up at Hogwarts to seek help in fighting Sauron, and they learn about magic wands and spells.
In a crossover fanfiction, black magic might be the catalyst for the meeting of the two worlds. Maybe a dark sorcerer in Middle - earth uses black magic to open a portal to the wizarding world of Harry Potter. This would bring about chaos as the characters from both sides have to deal with this new and unfamiliar form of black magic. The wizards from Hogwarts may be shocked at the more primal and ancient black magic they encounter in Middle - earth.
A really interesting way would be if there was a prophecy in both worlds about an immortal being who would bring balance. A character from Harry Potter, like Dumbledore who has some form of extended life through his powerful magic, and a character from LOTR, say Gandalf who is a sort of immortal spirit, could be the key players. They could discover that they are both part of this prophecy and have to work together. Their combined wisdom and power would be used to fight against the common threats in both worlds, such as the dark wizards in Harry Potter and the forces of Sauron in LOTR. This would involve a lot of world - building and character development as they bridge the gap between their two very different universes.
Yes, there might be. Some creative fanfiction writers like to blend different fictional universes. They could create a story where the concept of 'Harry Potter being the Master of Death' is incorporated into a 'LotR' - themed fanfic. It could be an interesting crossover with unique plotlines.
One great piece of fanfiction in this crossover might be 'The Magical Rings of Hogwarts'. It combines the magic systems of both universes in an interesting way. The characters from LOTR and Harry Potter interact in a believable manner, like Frodo and Harry becoming friends and sharing their experiences with the power of magic.
One idea could be that the One Ring somehow ends up in the world of Pirates of the Caribbean. Jack Sparrow, being the wily character he is, gets wind of its power and decides to either use it for his own gain or sell it to the highest bidder. The Fellowship, in turn, has to track it down in this strange new world full of pirates, sea monsters, and cursed treasures.
Well, it's quite an adventure. The characters face new powers and limitations as elves. The story might explore how their relationships evolve in this unfamiliar setting and how they handle the unfamiliar magic and creatures.
There are 'Lotr Harry Potter fanfiction' that focus on crossovers for epic battles. Imagine Voldemort's Death Eaters against Sauron's Orcs. These stories often play with the power levels of different magical beings from both series. Some fanfictions also explore the idea of Hogwarts being in Middle - earth or vice versa, which completely changes the dynamics of both the wizarding world and Middle - earth.