One possible plot line could be that the snake helps Harry in his battles against the Dark Arts. For example, it could use its unique abilities to sense danger and warn Harry in advance.
In the fanfiction, the friendship might also face challenges. Other students at Hogwarts could be scared or suspicious of Harry's snake friend. This could lead to situations where Harry has to defend their friendship, like when Draco Malfoy tries to get the snake removed from the school, believing it to be a dark creature. Harry then has to prove that the snake is good - natured and their friendship is based on mutual trust and respect.
In some 'Harry Potter is a pilot' fanfictions, there could be a plot where Harry has to transport magical creatures by air. He'd have to figure out how to keep them calm and safe during the flight. Also, perhaps he teams up with other wizard pilots to form a sort of magical air force to protect the wizarding world from threats in the air.
Imagine if the Dementors from Harry Potter somehow end up in New York where Friends is set. The Friends gang has to deal with the effects of the Dementors, like feeling all their happiness being sucked out. Phoebe, with her positive and somewhat otherworldly nature, could be the one to figure out how to repel them, maybe through her music or some kind of new spell she discovers.
One interesting plot line could be the exploration of the Black family heritage and secrets that the heir discovers. Maybe there are hidden magical artifacts or long - forgotten spells tied to the Black family that the heir has to uncover.
In certain fanfictions of 'Harry Potter Last Stand', the magic system could be expanded. There could be new spells or ways of using magic that are discovered during the last stand. For instance, a forgotten ancient magic might be unearthed by Hermione, which gives the good side an edge. And the after - effects of the battle on the wizarding world could be more thoroughly depicted, such as how they rebuild Hogwarts and deal with the remaining Death Eaters.
In some 'Harry Potter raised by magic fanfiction', there's a plot where Harry is raised by a group of house - elves. They use their own brand of magic to raise him. This gives Harry a different perspective on the magical hierarchy. He might grow up with a more empathetic view towards the so - called 'lower' magical beings. Also, he could have some unique magical abilities or knowledge that comes from the house - elves' magic.
Well, in some versions of 'Harry Potter gets a family fanfiction', Harry might be found by a family of magical creatures. For example, a family of centaurs could take him in. They would raise him with their own unique wisdom and values. This would give Harry a whole different perspective on the wizarding world and his place in it. He might learn their form of magic and use it to his advantage in the fight against dark forces.
One interesting plot could be the protagonist, as the King of Snakes, using snake abilities to solve mysteries in Hogwarts. For example, being able to communicate with the snakes in the Forbidden Forest to find out about hidden secrets or dark magic.
One interesting plot line could be exploring the true family heritage of a minor character. For example, Neville Longbottom's family might have some hidden magical lineage that gets uncovered in the fanfiction. This could lead to new powers or a different role for Neville in the wizarding world.
One interesting plot line could be the discovery of new magical abilities related to being the heir. For example, the character might be able to communicate with ancient Hogwarts spirits. Another could be a power struggle within Hogwarts as the heir's identity becomes known, with some seeing it as a threat and others as a hope for a new era.
It could be Nagini. Even though in the original series she was more of a servant to Voldemort, in the fanfiction, she could have a different personality and form a bond with Harry.