If Harry Potter can control people in the fanfiction, it might lead to some really unexpected alliances. He could convince some of the more neutral characters to join his side firmly. Also, it could make the other characters view him with a mix of fear and awe, changing the relationships he has. This new power would likely attract the attention of many, both good and bad, who would either try to use him or stop him, which would drive the plot in various directions.
Well, it could change the whole dynamic. He might use it to manipulate enemies, like making Voldemort's followers turn on him. This would speed up the end of the war perhaps.
Well, it might develop as a result of some new magic he encounters. There could be an ancient spell or a magical artifact that gives him the power to control sand. He then has to figure out how to use it. He may start with simple things like making sand swirl around his hand, and as he gets more used to it, he can do more complex things like creating sand barriers or even using the sand to communicate in some way.
Well, it could change the relationships in the story. For example, he might use it to make enemies become allies, like turning some Death Eaters to his side. This would completely shift the power balance in the fight against Voldemort.
Well, it could change the whole sequence of events. For example, he might be able to go back in time to prevent certain tragedies from happening in the wizarding world. This would rewrite a lot of the original story's plotlines as we know them.
Maybe he accidentally finds out when he is near some magnetic objects in Hogwarts. For example, he might notice that he can make the metal keys move towards him without using magic spells he already knew. It could be during a time when he is exploring an old, forgotten part of the castle where there are a lot of metal objects and strange magnetic fields.
In some fanfictions, it could be through an accidental encounter. Maybe he was in a situation where metal objects started to react to him unexpectedly, like when he was near a bunch of keys and they suddenly started to move towards him. This made him realize that he had this strange new power.
Perhaps he has a strange dream where he's in a world made entirely of shadows and he can manipulate them freely. When he wakes up, he starts to experiment and finds out that he can actually do the same in the real world. He might start with small things like making the shadow of a quill move on his desk, and gradually discovers the full extent of his power.
Perhaps it's through an accidental encounter with a powerful magical plant. He tries to interact with it in a normal way but ends up influencing its growth and behavior. This unexpected event makes him aware of his unique power to control nature. For example, he might touch a withering plant and suddenly it springs back to life and starts to grow rapidly under his touch.
Well, in such a fanfiction, he might control space through his magic wand. Maybe he uses a special spell that he discovers or invents, which allows him to manipulate the fabric of space, like creating portals or warping distances.
It has a huge impact on the plot. First, he could use his time - controlling ability to gather more information. For instance, he could find out Voldemort's secrets earlier. He might also be able to change the outcome of battles. If he went back in time to a battle, he could warn the Order of Phoenix about the Death Eaters' plans. In terms of character development, he could become more confident and wise as he experiences different timelines. This new ability would make him a much more powerful force in the wizarding world, and the fanfiction would explore how he uses this power for good or bad.
One consequence could be that he loses the trust of his friends. They might be afraid that he could control them at any time.