In a fanfiction where Harry Potter is turned into a wraith, his magic would likely change too. He might be able to use his wraith form to access places that were previously inaccessible. Maybe he could enter the Forbidden Forest without being detected by the creatures there. But on the downside, he'd be in a constant state of being not quite alive and not quite dead. This could mess with his mind, and he'd have to struggle to hold on to his identity while dealing with his new form.
The story could progress with Harry trying to find a way to turn back. He might search for ancient spells or magical artifacts that could reverse his condition. His friends would be desperate to help him, and they'd start their own investigations. Maybe Hermione would scour the library for any information on wraiths and how to reverse the transformation.
Well, he'd probably have to deal with a whole new set of powers and weaknesses. He might be able to move faster and have enhanced strength like regular vampires. But he'd also have to face the thirst for blood, which would be a huge struggle considering his moral code. And his relationships with his friends would change. They might be scared of him at first, or he might have to keep his new condition a secret from them to protect them.
In such a fanfiction, Harry might gain the physical abilities of a basilisk. He could have its incredible strength and speed. Maybe he would also inherit the basilisk's venomous nature, which could be both a weapon and a danger to those around him. Also, his appearance would change drastically, with the snake - like body and menacing eyes.
If Harry Potter became a vampire in fanfiction, his relationships would change a great deal. His friends might be scared of him at first. Hermione would probably be researching like crazy to find a way to reverse it or at least help him manage. Ron might be more hesitant to be around him, but still loyal in his own way.
In the 'Harry Potter gets turned into a cat' fanfiction, there could be a lot of comical situations. Imagine Harry trying to attend classes as a cat. He might jump on desks, knock over ink bottles, and cause chaos in the classroom. His professors would be very confused about this strange cat's behavior. And when it comes to fighting Voldemort, it would be a very different scenario. He might use his cat - like agility to dodge spells, but also have to find a way to cast his own magic in this new form.
He might also be a bit confused at times. Some fanfictions deviate a lot from the real events in his life. For example, if there's a fanfiction where he has a completely different upbringing, it would be strange for him to read about. He could also feel a sense of flattery that so many people are interested in his story and want to create their own versions of it.
In such a fanfiction, Harry might face a whole new set of challenges. For example, he would have to deal with the different ways people treat him as a girl. His friends might be initially shocked but then gradually accept this new version of him. He could also use this new form to his advantage in some situations, like getting closer to certain characters who were previously more guarded around him.
He might be really surprised. Fanfiction often contains different interpretations of the characters and the story. He could be amused by some creative ideas, or perhaps a bit confused if the fanfiction goes too far from the original story he knows.
In a 'Harry Potter in Gotham' fanfiction, Harry might team up with some of Gotham's heroes. For example, he could share his knowledge of magic with Batman. Harry's magical creatures knowledge could also come in handy. He might introduce Thestrals to Gotham as a new form of transport for the heroes during emergencies. Also, his ability to communicate with snakes could potentially help in dealing with some of the more reptilian - like villains in Gotham.
The idea of Harry Potter with a gun is quite interesting. One possibility is that he gets the gun from the muggle world accidentally. He might initially be confused about how to use it but then realizes its potential. This could lead to new alliances in the wizarding world. Some wizards might be intrigued by this new weapon and want to learn more about muggle technology, while others might be afraid and try to confiscate the gun from Harry.