Some authors might make it a slow and gradual process. They'll show Harry noticing small differences in his Patronus over time. For instance, its color might start to fade or change slightly at first, and then as the story progresses, the form itself starts to transform. This gives a sense of mystery and builds suspense in the story.
In some fanfictions, Harry's Patronus could change because of a magical artifact. Maybe he discovers an ancient amulet that has the power to influence magic within him. As he gets closer to the amulet and starts to understand its power, his Patronus begins to change, say from a stag to a griffin, which could represent the new power and knowledge he has gained from the amulet.
I've read a fanfic where the main character has a fox patronus and they use it to explore the Forbidden Forest. It was really exciting as they discovered new magical creatures with the help of their patronus's senses.
In some Harry Potter fanfictions with a fox patronus, the author might explore the symbolism of the fox. The fox is often seen as clever and sly in muggle folklore, so perhaps in the fanfic, the character with the fox patronus uses these traits to outwit dark wizards or solve mysteries within Hogwarts. For example, they could use their fox - like cleverness to figure out the secrets of the Chamber of Secrets in a new and different way than what was shown in the original books.
A pegasus Patronus is also a great concept in fanfiction. Pegasus represents grace and freedom. A character with a pegasus Patronus might be someone who values these qualities. They could be the type of person who is always looking for a way to break free from constraints, whether it's social norms or dark magic threats in the wizarding world. This Patronus could also suggest a connection to the skies and a more spiritual side of magic.
In some fanfictions, the Basilisk could be reimagined in a different light. Maybe it's not just a mindless monster but has some sort of deeper purpose or connection to the Patronus magic. For instance, a fanfic could show that the Basilisk was once used in an ancient spell that now affects how modern - day Patronuses work. This would add a whole new layer of mystery and intrigue to the Harry Potter universe.
Well, a Thestral Patronus in fanfiction might be a symbol of the character's ability to face their fears. Since Thestrals are invisible to those who haven't witnessed death, a character with a Thestral Patronus could have a special understanding of mortality. It could be used in the fanfic to show that the character has a complex personality. They are not just the typical 'good' or 'bad' but have a depth that comes from experiencing something as profound as death. This kind of Patronus could also be a way for the author to explore themes of grief and acceptance in the story.
One interesting Harry Patronus fanfiction could be where Harry discovers a new form of Patronus magic that has been long forgotten. This could lead to him having to face new dark forces with this enhanced power.
One common theme is the power of hope. Harry's Patronus often represents hope in the face of darkness, like in the original series. Fanfictions usually expand on this, showing how his Patronus can inspire others as well.
One possible fanfiction could be where Harry has to conjure his Patronus in the courtroom to prove his innocence. Maybe he's wrongly accused of using dark magic, and the Patronus is the only way to show his pure intentions.