Hermione and Sandy could be great for a crossover. Hermione's intelligence and love for knowledge could be paired with Sandy's scientific know - how. They could collaborate on some sort of underwater - land hybrid project, perhaps creating a new kind of magical - scientific device that works both in Hogwarts and in Bikini Bottom.
Dumbledore and Mr. Krabs would make an interesting pair. Dumbledore's wisdom and calm demeanor could be a foil to Mr. Krabs' money - grubbing ways. Maybe Dumbledore could teach Mr. Krabs about the value of things other than money, while Mr. Krabs could show Dumbledore some unique business strategies from the underwater world.
Loki and Draco Malfoy would be a likely crossover. Loki is the mischievous god in the MCU, and Draco is a bit of a troublemaker in the Harry Potter world. They could team up and cause all sorts of chaos. Maybe Loki would teach Draco some of his more devious tricks, and Draco could introduce Loki to the pure - blood ideology of the wizarding world, which could lead to some really interesting storylines.
Ciri and Daenerys Targaryen. Ciri has magical powers and is a strong female character. Daenerys has her dragons and is a powerful leader. They could meet and form an alliance. Ciri might be interested in Daenerys' dragons and Daenerys could be intrigued by Ciri's magic. Together they could change the power dynamics in a fanfiction world.
Elsa is quite popular. Her ice powers make for an interesting contrast with the magic in Harry Potter. Hermione is also a common character to cross over. Her intelligence and love for knowledge would make her curious about the world of Frozen 2. Harry Potter himself is often used in crossovers as well, as his heroic nature can fit into the story of Frozen 2 easily.
Harry Potter and Link are two of the most popular characters to cross over. Harry, with his magical abilities and experience in fighting dark forces, and Link, the hero with his sword - fighting skills and courage. When combined, they can create some really exciting storylines.
Harry Potter himself is often a popular choice to cross over. His courage and magical abilities make him a great addition to the Narnian world. Also, Aslan from Chronicles of Narnia is sometimes brought into the Harry Potter universe. His powerful and wise nature can bring a new perspective to the wizarding world.
Hermione Granger is also very popular. Her intelligence and knowledge of magic would be valuable in Narnia. She could study the magic in Narnia and perhaps find ways to combine it with what she already knows from Hogwarts.
Harry Potter and Ben Tennyson are obviously very popular. Harry's role as the hero in the wizarding world and Ben's as the wielder of the Omnitrix make them natural choices for crossovers. Hermione is also often included as her intelligence could be used to figure out the science behind the Omnitrix.
In 'harry potter flash crossover fanfiction', Harry Potter and the Flash are the obvious front - runners. But aside from them, characters like Sirius Black could be interesting. He has his own set of skills and a rather rebellious nature. Meeting the Flash could result in some exciting adventures. Ginny Weasley, with her courage and talent in Quidditch, might also be a character that fans like to cross over. She could potentially learn some new skills from the Flash or vice versa. And then there's Professor Snape. His complex personality and his skills in potions and the dark arts could create some intense and thought - provoking crossovers with the Flash.
Harry Potter himself is often a popular choice. He can be thrown into the chaotic world of Warhammer and his skills and values are put to the test. Another is Dumbledore. His great wisdom and powerful magic could be an interesting match against the dark forces in Warhammer.
Hermione Granger and Hera Syndulla are often crossed over. Hermione's intelligence and vast knowledge of magic can be paired well with Hera's leadership and piloting skills. Also, Han Solo and Ron Weasley are popular choices. Their roguish charm and sense of humor are quite comparable, and fanfiction writers like to explore how they would get along or what kind of adventures they would have together.