What could happen when Harry talks to the troll in the fanfic?

He might approach it cautiously. After all, trolls are dangerous creatures. He could start by speaking in a calm voice, trying not to startle it.

Well, he might try to tame the dragon. In some fanfictions, Harry could use his magic skills to communicate with the dragon on a deeper level, perhaps to gain its trust and make it an ally.

Perhaps Harry Potter talks to the dragon to enlist its help in finding a powerful magical object. Dragons are known to guard treasures. He could be on a quest for a Horcrux or some other important item. The dragon might initially be hostile but as they talk, it starts to trust Harry. Their conversation could involve exchanges about the power of magic, the dragon's own experiences in the magical world, and how they can both benefit from working together.

In some fanfictions, Harry might seek Snape's advice on how to deal with the remaining dark magic threats. Since Snape was so knowledgeable, his portrait could offer unique insights.

Well, he might be tempted by the dark magic within the Horcrux. It could try to manipulate him, maybe show him false visions of power or ways to defeat Voldemort that are actually leading him astray.

In fanfiction, when Hermione talks to a Death Eater, she might try to persuade the Death Eater to abandon their dark ways. For example, she could use her intelligence and knowledge of the wizarding world to show the Death Eater the error of their beliefs. Maybe she would bring up the harm that Voldemort has caused and how following him is only leading to destruction.

Maybe Harry discovers a new type of snake with magical abilities. For example, it could be a snake that can turn invisible at will. This would be really cool as it could add a new dimension to the wizarding world's magical creatures.

Well, he might be given a dangerous mission. Maybe he has to infiltrate a Death Eater stronghold or protect a crucial magical artifact.

One possible plot could be that Harry tries to reason with Voldemort about the futility of his dark ways. He might talk about how much destruction Voldemort has caused and how many lives have been lost. Harry could also try to appeal to any remaining shred of humanity in Voldemort, perhaps by bringing up his own orphan status and how they both lost their parents in a way, though for very different reasons.

It could be about Harry having a unique ability to communicate with dragons and using this to solve various problems in the wizarding world. Maybe he teams up with dragons to fight dark forces.