The plot could be changed as Harry might be able to access places or information that others can't. Like, there could be a secret Parseltongue - locked room in Hogwarts, and he is the only one who can open it. This could lead to new adventures and revelations in the fanfiction.
It can change the plot by making him an outcast among his peers. For instance, his friends might be wary of him at first.
His ability can also change the plot in terms of how he interacts with the wizarding world. Since Parseltongue is associated with the Dark Arts in the eyes of many, he might have to constantly prove that he is not on the side of the dark. This could create a lot of tension and conflict, as well as opportunities for character growth and new storylines.
It can introduce new conflicts. If Draco's Parseltongue ability is discovered, it could lead to suspicion from other characters, especially those who are wary of anything related to dark magic. This could create a rift between Draco and his friends or family within the fanfiction world.
Well, at first, Harry would probably be very wary of Draco. Since he has his own history with Voldemort and Parseltongue, he'd see Draco's new ability as a sign of potential danger. However, as time goes on, if Draco is trying to use his Parseltongue for good, like communicating with snakes to find out about dark magic threats, Harry might start to trust him more. Their relationship could shift from one of enmity to an uneasy alliance. They could even start to understand each other's insecurities better. Harry has always been an outcast in some ways, and now Draco is too with his strange new ability.
One idea could be that Draco's ability to speak Parseltongue gets him into trouble with the Ministry of Magic which is still very much on edge after Voldemort's fall. They suspect him of dark intentions. Another could be that he uses it to secretly communicate with a hidden basilisk in Hogwarts, left behind from the Chamber of Secrets era. And he might be trying to protect it or use it for some sort of personal gain in the wizarding hierarchy.
In some fanfictions, Harry's Parseltongue - only speaking ability might put him in a difficult situation with the Ministry of Magic. They might suspect him of being too closely related to dark magic. However, Harry uses this ability to prove his innocence by communicating with a snake that witnessed a crime committed by a Death Eater, and thus he helps in the fight against the remaining dark forces.
Well, it could make some characters more wary of her. For example, those who are prejudiced against Parselmouths might view her with suspicion. However, it could also bring her closer to Harry, as he's the only other known Parselmouth among their group. They might bond over this unique ability and share their experiences related to it.
In fanfiction, Harry's snake - communication ability can completely shift the plot by introducing new magical elements. Since snakes are associated with Slytherin, Harry might discover a long - lost Slytherin spell or magic that can only be accessed through communication with snakes. This could be a powerful weapon against Voldemort. He might also use it to bridge the gap between the different houses at Hogwarts. For example, by showing that not all snakes are bad, he could encourage better relations between Gryffindor and Slytherin. This would lead to a more united front against the common enemy, Voldemort.
His friends would be both amazed and a bit envious. Hermione might be very interested in studying this new aspect of magic related to his ability. Ron, on the other hand, would probably be in awe and might ask Harry to use his ability to find some cool magical animals to play with. It could also make them more protective of Harry, as his ability could attract unwanted attention from those who might want to use it for bad purposes.
Well, in some versions of this fanfiction, Harry might discover it by accident. For example, he could be in a situation where he's near a dragon and instead of the usual fear or aggression from the dragon, it seems to be communicating with him in a strange way. Maybe the dragon's eyes seem to be trying to convey a message, and Harry just somehow understands it, like he has an innate sense that he can pick up on the dragon's thoughts.
Well, it could change the plot in many ways. For example, he might be able to negotiate with them. Maybe he can convince them not to attack people, which would make Hogwarts a much safer place. He could also learn more about their origin and motives directly from them, instead of just speculating as others do.
Maybe she was exposed to some ancient magic. It could be that she was in a place where there was a strong Parseltongue - related magic, and it somehow influenced her.