Ron could be there to support Harry. He's brave too and could distract the dragon while Harry prepares a powerful spell. Also, Dumbledore might offer some wise advice from the sidelines if he's involved in the story.
Hermione could help. She's very smart and could research about the dragon's weaknesses.
Well, in such a fanfiction, Harry could have found a magical fire - producing object that gives him the ability to fight the dragon with fire. He might have to learn how to handle this new power quickly while in the heat of the battle. The dragon, on the other hand, would use its natural abilities like flying and breathing fire in return. It would be a battle of wits and power.
Hermione could be a great help. She's very knowledgeable about magic and could research how to properly care for a newly hatched female dragon.
Hermione would most likely help. She's always been there for Harry, and with her vast knowledge from books, she could offer a great deal of advice on how to take care of the dragon egg. Ron might also be involved. Despite his initial fear of things, he has a brave heart and would probably stand by Harry's side.
Dumbledore could also play a role. Even if he's not alive in the normal sense, his spirit or some form of his magic could guide Harry. He might have known about the connection between Harry and Excalibur all along and left behind some hints or instructions for Harry to follow.
His friends from Hogwarts like Hermione and Ron would most likely support him. They have always been by his side through thick and thin in the original story, so in the fanfiction, they would continue to support Harry in his fight against the Ministry.
In these fanfictions, the theme of the power of knowledge often comes up. Harry has to use his knowledge of dragons, which he might have learned from books like 'Fantastic Beasts and Where to Find Them', to find the dragon's weaknesses. Additionally, the theme of heroism is common. Harry is seen as a hero for taking on the dangerous dragon to protect the wizarding world or to achieve some important goal.
In this fanfiction, Harry might use his magical skills like the Patronus charm to fend off the dragon. Maybe he'd also rely on his broomstick flying skills to dodge the dragon's attacks.
His friends from Hogwarts, like Ron and Hermione, are likely to help. Ron could bring his family's practical knowledge of wizarding homes and Hermione would contribute with her extensive research skills.
It could be some Death Eaters who are causing chaos at the World Cup. They might be trying to disrupt the event and target Harry.
It could be a wild dragon from the Forbidden Forest that had some sort of encounter with one of Harry's ancestors. Maybe a female dragon who was drawn to the magic of a powerful wizard in Harry's family tree.