The Harry Potter universe might see an influx of new magical knowledge from the Star Wars galaxy. Since Harry has interacted with it, there could be new spells or magical concepts brought back. In the Star Wars universe, without Palpatine, Luke Skywalker and the other Jedi might not have to face as many challenges. However, the dark side would still be present, and new threats could emerge. And the relationship between the two universes could become a major point of study and diplomacy for both sides.
It could be that a powerful wizard in the Harry Potter universe sends Harry to defeat Palpatine for some greater good. Harry's quick thinking and his array of spells like Expelliarmus or the Killing Curse (although he hates to use it) could potentially be used against Palpatine. Since Palpatine is used to dealing with lightsabers and the Force, Harry's magic could catch him off - guard.
One consequence could be that the Joker's followers would be out for revenge. They might target Harry Potter or his friends if they also exist in that fanfiction world. Another consequence could be that the balance of power in the Joker's world is completely disrupted. There could be a power vacuum that other villains or even some anti - heroes might try to fill.
He might gain more respect from his peers. After all, killing the Basilisk is no small feat. His friends would probably look up to him even more, and his reputation in Hogwarts could soar. He could also become a bit of a legend among the younger students.
The wizarding world would likely be in a state of shock and then celebration. People would start to see Azkaban in a new light, perhaps no longer as just a place of horror but also as the site where the great evil was finally vanquished.
Well, it could be that the magic from Harry Potter's world and Android 18's advanced technology somehow interact. Maybe the spells in Harry Potter are used to enhance or modify Android 18's abilities. For example, a spell could be cast on her to make her energy blasts more powerful or her speed even faster.
There could be some negative consequences too. Maybe the dragon had some kind of magical protection or was under the care of a powerful wizard or creature. Harry might then face the wrath of those who were protecting the dragon, leading to him having to go into hiding or facing dangerous challenges. Also, the act of killing a dragon, even in self - defense, might make some more sensitive wizards view him in a different, less favorable light.
It could lead to a major shift in the power balance in the wizarding world. Without Hermione's intelligence and strategic thinking, the good side might struggle more against any potential threats. Also, Ginny would probably be deeply affected, as she is close to Harry and Hermione. She might be torn between her loyalty to Harry and her horror at what he has done.
In these fanfictions, they blend by sharing certain characteristics. For example, the loyalty and camaraderie among the characters in both universes are emphasized. In Harry Potter, it's the loyalty among the students of Hogwarts and the Order of Phoenix. In Kancolle, it's the bond between the shipgirls. This common trait can be a basis for the two universes to interact, like the shipgirls and the wizards/witches working together based on mutual trust.
In the fanfiction, there could be a range of consequences. On one hand, he could be seen as a hero by his fellow students. They might admire his bravery and his ability to take on a dangerous troll. However, the teachers may be more cautious. If Harry used excessive force or magic that was not in line with the school's code of conduct, he could be given detention or even face a disciplinary hearing. Also, depending on how the troll was killed, there could be some magical fallout. For example, if he used a very dark spell, it could have an effect on his own magical core or his relationship with magic in general. Moreover, the death of the troll might also attract the attention of other dark creatures or forces that were somehow related to the troll, putting Harry in further danger.
One consequence could be that he becomes a hero among his peers. Everyone in Hogwarts might look up to him even more. The other students could see him as a real dragon - slayer, which gives him more popularity and respect.