In the 'Harry adopted by the Malfoys' fanfiction, one possibility is that Harry would receive a very different kind of magical education. The Malfoys might try to mold him into a Slytherin - like wizard, but Harry's own Gryffindor - like courage would constantly be at odds with that. Also, his relationship with Draco could be very complex, ranging from initial rivalry as they are brought up in the same household to a possible understanding and even friendship later on.
Well, one possibility is that Harry would grow up with a very different set of values. The Malfoys are known for their pure - blood supremacist views. But perhaps, deep down, Harry could influence them to be a bit more accepting. He might learn dark magic quicker than in the original story, but also struggle with his own sense of right and wrong as the Malfoy values clash with what he feels inside.
His personality would likely be a blend of his natural Gryffindor traits and the influence of the Malfoy family. He might become more guarded and calculating at times, due to the Malfoy's sly nature. But his underlying sense of justice and loyalty would still shine through. For example, he might be more hesitant to trust people initially compared to in the original story.
Well, in such a fanfiction, Harry might be given a very different education. The Malfoys could try to indoctrinate him with pure - blood supremacist ideas at first. But as he grows, he might rebel against it. He could also be exposed to a different social circle within the wizarding world. Maybe he would have more interactions with other Slytherin families and this would change how he views things like House rivalries. And his relationship with Dumbledore would be very strained as the Malfoys are not on good terms with Dumbledore.
He might become more refined in his manners. The Malfoys are a very proper pure - blood family, so Harry would likely be taught to act more like them. For example, he'd probably have better table manners and a more sophisticated way of speaking.
In such a fanfiction, Harry might gain access to ancient magic knowledge. The founders, being from a different era, could teach him things not available in his own time. He may also experience a very different Hogwarts, perhaps one more in line with the founders' original vision.
In the 'Harry adopted by the Winchesters' fanfiction, there are a lot of possibilities. Harry could bring his knowledge of potions and magical artifacts to the Winchesters. This could be useful in dealing with some of the more dangerous supernatural threats. The Winchesters, on the other hand, could teach Harry about survival in a more 'normal' but still dangerous world. Their skills in tracking, weapons handling, and understanding human nature could be invaluable to Harry. Also, the relationships between Harry and the individual Winchesters would be complex and evolving. There could be moments of conflict as they come from very different backgrounds, but also moments of great bonding as they face various challenges together.
If Harry was adopted by the Joker in fanfiction, it could lead to some really interesting character development. Harry might start to develop a warped sense of humor and a disregard for the law like the Joker. On the other hand, he could also be a source of conflict within the Joker's world. Maybe Harry would try to resist the Joker's influence and secretly work towards bringing him down. It would be a battle of wills between the two, with Harry having to use his wits to survive in the Joker's crazy world.
In such a fanfiction, Harry's life would be extremely different. Bellatrix is a Death Eater, so Harry might be indoctrinated into dark magic. However, his strong will from his original upbringing might resist this. He could be in a constant internal struggle between the light he was initially inclined towards and the dark teachings of Bellatrix.
In such a fanfiction, Harry might be raised with a very different set of values. Voldemort could try to mold Harry into his own image, perhaps teaching him dark magic. But Harry might also secretly hold on to his own sense of good. For example, he could use the knowledge Voldemort gives him to ultimately turn against him.
In such a fanfiction scenario, Harry might have a very different upbringing. He could be exposed to a more academic and Muggle - centered environment. The Grangers, being dentists, might encourage him to pursue a more traditional Muggle career while still being aware of his wizarding heritage. He would probably grow up with a strong sense of discipline and study habits from them.