A popular one is 'Naruto's Witch Encounter'. Here, Naruto meets a young witch during one of his missions outside of the village. She has a special mission of her own that somehow gets intertwined with Naruto's goals. As they work together, they discover new abilities within themselves and a deep connection forms between their two very different worlds.
For the Naruto characters in this crossover, you can start by emphasizing how they react to the witchcraft. For example, Naruto might be initially in awe but quickly see the practical applications of magic in his fights. His determination could lead him to try and learn some basic spells. As for the witches, give them distinct personalities. One could be a haughty witch who looks down on the 'primitive' ninja ways.
A more complex scenario could involve a group of witches who are at war in their own realm. They decide to bring some of the powerful Naruto characters into their world to fight on their behalf. Naruto and his friends would have to adapt to the strange magic - filled environment and the political intrigue of the witches' war.
Friendship and cooperation are big themes. Naruto, being a character who values friendship highly, forms bonds with witches in these crossovers. They have to learn to trust each other despite their differences. Also, identity is a theme. Witches may have to hide their true identities in the Naruto world, and Naruto characters might question their own identities when exposed to the new and strange world of witches.
One interesting idea could be that Naruto somehow gets transported to Sabrina's world. He could use his ninja skills in the magical world of Greendale. For example, his speed and stealth could be useful in the spooky forests around Sabrina's town. Another idea is that Sabrina uses her magic to help Naruto in his battles in the Naruto universe. Maybe she could use her magic to heal some of his injured friends or to create illusions to deceive his enemies.
First, you need to understand the Scarlet Witch's character well. Know her powers, her backstory, and her personality traits. Then, choose the other universe or character you want to cross her over with. For example, if it's the Harry Potter universe, think about how her magic would compare to Hogwarts magic. Next, come up with a plot that makes sense for both universes. Maybe she's there to solve a mystery that affects both worlds.
One great Scarlet Witch crossover fanfiction is 'Scarlet Witch in the DC Universe'. It's really interesting to see how her powers interact with the different rules and characters in the DC world. Another one is 'Scarlet Witch and the Doctor' which combines her story with the Doctor from Doctor Who. The unique settings and crossovers in these fictions make them stand out.
Often, there's the theme of self - discovery. In 'the worst witch crossover fanfiction', characters are put in situations outside of their comfort zones. For example, Mildred Hubble might find herself in a world where her magic is not as powerful or is seen in a different light. This forces her to reevaluate who she is as a witch and grow as a character.
One common theme is power struggle. Since the Witch King is a powerful figure, when he crosses over, there's often a battle for dominance with other powerful characters in the new world.
A witch character with the power to create illusions that are even more powerful than those in the ninja world would be really fascinating. She could use these illusions to deceive Naruto's enemies or even to teach Naruto new ways of using illusions himself. Also, a witch who has a deep connection with nature and can use nature's magic in the middle of the ninja world's battles would be quite an interesting addition to the fanfiction.