One possible consequence is that his perception of reality changes completely. He may start to question everything he knew before going through the mirror. In the fanfiction world, this could lead to him making different choices in his relationships with his friends like Ron and Hermione. He might become more distant from them as he tries to figure out this new reality, or he could grow closer as they help him understand what he has experienced.
He might gain some extraordinary magical abilities. For example, he could be able to control time or have a deeper understanding of magic spells that were previously difficult for him.
Well, he might accidentally bring some of the dark forces from his world to Remnant. Or, on the other hand, he could bring new hope and ideas to fight the existing threats in Remnant. His presence could also cause some political unrest as the different factions in Remnant might try to use him for their own gains. And of course, his own journey of self - discovery would be completely different in this new world.
His friends could be disappointed in him. In the original story, the Yule Ball was something that his friends were looking forward to, and if he doesn't go in the fanfiction, they might feel let down. This could lead to some strain in their relationships. Additionally, not going to the ball might mean that Harry doesn't get to show off his dancing skills (if he had any in the fanfiction), and he might lose some popularity among the students who were expecting to see him there.
Socially, his status as a hero might change. Some might see him as weakened and no longer the invincible hero. This could lead to a shift in the wizarding community's perception of him, and he might have to work hard to regain his former standing.
Well, if Harry gets rid of Snape, he might face backlash from the Slytherin house. Snape was a Slytherin and had his supporters there. They could make Harry's life difficult in various ways, like spreading rumors or trying to undermine his achievements. On the other hand, Harry might find new allies. Those who were secretly afraid of Snape but couldn't do anything might now side with Harry. But he also has to be careful not to let this new - found power go to his head, or he could end up making more enemies in the long run.
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.
One possible consequence is that the wizarding world might see Harry as a hero even more than before. After all, dementors are very dangerous creatures, and if he manages to destroy them, it's a huge accomplishment.
The wizarding world might be in shock. People who have always seen Voldemort as the ultimate evil would be confused. They would have to re - evaluate their views on Voldemort. Harry, on the other hand, would be in a very strange situation. He might be distrusted by some of his friends who think he has made a deal with Voldemort.
One consequence could be that the wizarding world falls back into chaos and fear. Voldemort would likely start his reign of terror again, targeting those who opposed him before. He might also try to seek revenge on Harry for initially defeating him.
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.