If Harry Potter were a villain in fanfiction, it would change everything. Firstly, his friends like Ron and Hermione would be in a really difficult situation. They might have to fight against him, which would be heart - breaking for them. Harry could start to use dark magic without hesitation. He might try to rewrite the wizarding world's rules according to his own will, causing a great upheaval in the whole magical community.
Well, if Harry Potter becomes a villain in fanfiction, it would be a complete subversion of the original story. He might use his powerful magic skills to dominate Hogwarts instead of protecting it. He could form alliances with the dark forces that he once fought against. Maybe he would start to spread fear among the students and teachers, and turn the school into a place full of chaos and tyranny.
In such a fanfiction, Harry might gain the ability to rise from ashes, literally and metaphorically. He could have the power of regeneration and immortality like a Phoenix. This would change his battles, for example, he could fearlessly face Voldemort as he could always come back even if defeated. His relationship with his friends might also change. They would see him as an even more extraordinary being, and he might have to deal with their awe and a bit of distance that could come from his new form.
Well, it could be really interesting. Harry Potter, with his magical background from Hogwarts, would find the world of Witchers quite fascinating. He might be intrigued by the Witchers' potions and their unique way of fighting monsters. Maybe he'd try to combine some of his spells with the Witchers' combat skills. For example, he could use a Patronus charm while also slashing at a monster with a Witcher's sword. And he'd surely be interested in the different kinds of monsters in the Witcher world compared to the ones he faced in the wizarding world.
Well, it could be a very dark plot. Maybe Harry is under some dark magic influence that makes him lose his mind and start killing. It would completely change his character from the original story.
If Harry Potter becomes an obscurial in fanfiction, the story could take a very different turn. He might not be as eager to attend Hogwarts as he was originally. The Dursleys might have an even worse time with him because his obscurial powers could lash out. At Hogwarts, teachers would be extremely concerned. Snape, for instance, might be even more critical of him, seeing him as a potential danger. And Harry would have to learn to control this new and dangerous aspect of himself.
In such a fanfiction, Harry Potter becoming a Darth Vader fan could lead to him adopting some of Vader's more authoritarian and decisive ways. He might start to use more forceful methods to deal with his enemies in the wizarding world, which would surely cause a stir among his friends and foes alike. For example, instead of relying solely on magic spells in a traditional way, he could be influenced by Vader's use of the Force and try to develop something similar in the magical realm.
In this fanfiction, the plot might show Harry's transformation into a Dark Lord as a result of some major betrayal in the wizarding world. For example, if the Ministry of Magic turned against him or if his friends were seriously harmed by the 'good' side. He could then start to see the power of the dark side as a means to exact revenge and reshape the wizarding world according to his own vision. He might recruit former Death Eaters or create his own dark followers.
In some fanfictions, if Harry Potter becomes a warlock, he might gain even more powerful magic. He could have greater control over spells and be able to perform magic that was previously thought impossible. For example, he might be able to manipulate time in a more complex way or have the power to instantly transport himself anywhere in the wizarding world without the need for a Portkey or Apparition.
If Harry Potter becomes god in fanfiction, he might completely reshape the magical world. He could rewrite the laws of magic, perhaps making it more accessible and less dangerous. He could also bestow extraordinary gifts upon his friends. Hermione might gain the ability to instantly understand and master any spell or bit of knowledge, and Ron could become an unbeatable warrior with superhuman strength in the face of any danger.
In this kind of fanfiction, Harry might teach his children magic in a very different way from how he was taught. He would be extremely protective, having faced so many dangers himself. Maybe he'd pass on the lessons he learned from his own battles, like the importance of friendship and courage.
If Harry Potter becomes the Joker in fanfiction, he would probably start to question all the values he once held. The Joker is all about subverting order, so Harry might begin to undermine the Ministry of Magic and other institutions. He could use his knowledge of magic to play cruel pranks on people, not the innocent kind of pranks he used to do. His Gryffindor courage could be twisted into a reckless disregard for the safety of others.