The White Walkers could be the main antagonists. Since Jon Snow has found a dragon, they might see it as a threat to their plans of taking over the Seven Kingdoms. They would try to kill the dragon and Jon Snow to ensure their dominance remains unchallenged.
In this fanfiction, it could be that the dragon is actually a key to unlocking some ancient magic or prophecy. Jon Snow, finding the dragon beyond the Wall, realizes its significance. He teams up with the dragon, and together they embark on a journey to find out more about this magic. Along the way, they face many challenges, both from the natural elements beyond the Wall and from the political intrigue brewing in the Seven Kingdoms as word of the dragon spreads.
Daenerys Targaryen could be one to help. Since she has experience with dragons, she could give Jon Snow advice on how to care for the egg and hatch it.
An author who has a passion for exploring alternate storylines in the 'Game of Thrones' world could be the one to write an amazing 'Jon Snow finds a dragon' fanfiction. This person might be someone who was disappointed with the original show's ending regarding Jon Snow and wants to give him a more epic and dragon - filled adventure. They could draw on different elements from the books and the show to create a unique and engaging story.
It could be a dark wizard or sorcerer who wants the dragon egg for its power. They might try to steal the egg from Bella.
There could be a group of magical creatures who see the snake as an abomination or a threat to their kind. They would try to destroy the snake and Harry would have to protect it. These creatures could be from a part of the Forbidden Forest that has not been explored much in the original books and they have their own set of rules and magic which makes them a formidable antagonist.
Jon Snow could discover that the dragon has some sort of special connection to his true heritage. Maybe it was left there by his Targaryen ancestors. The dragon could help him uncover secrets about his family and his place in the world. He may also face challenges in controlling the dragon at first, but with time, he masters it and uses it to change the fate of Westeros.
Well, in this fanfiction, it's possible that the dragon egg has some special connection to Jon Snow's true parentage. It could be a sign of his Targaryen heritage, if we follow the theories. He could then use the dragon that hatches from the egg to fight against the White Walkers, as dragons are very powerful creatures in the 'Game of Thrones' universe.
One common theme is adventure. Jon's discovery of the dragon eggs often leads him on a series of exciting adventures as he tries to protect or hatch the eggs. Another theme is power. Dragon eggs symbolize great power, so stories often explore how Jon deals with the implications of having such power at his disposal.
Obviously, Arya and Jon are the main characters. Arya, with her unique skills and strong will, and Jon, known for his leadership and sense of duty.
The North would surely support him. They have always seen him as one of their own and a great leader. Also, the wildlings might back him, considering he has a history of working with them and understanding their plight. Davos Seaworth would most likely be on his side as well, given his loyalty to Jon in the past.