Another interesting plotline could be the discovery of how Harry got two fathers in the first place. It might involve some long - lost magic or a strange prophecy that led to this unique situation. This could open up a whole new world of exploration in the fanfiction, delving into the lore of the Harry Potter universe.
One possible plotline could be how Harry deals with the different parenting styles of his two fathers. For example, one might be strict about magic studies while the other is more lenient, creating a dynamic where Harry has to navigate between them.
It could also be Hagrid and James Potter. Hagrid was always there for Harry, taking him to Diagon Alley for the first time and showing him care. In a fanfiction world, he could be one of Harry's fathers with James Potter being the other.
Perhaps in the fanfiction, the two dragons have different personalities. One could be more aggressive and the other more cautious. This causes Eragon to have to balance their natures while training them, leading to a whole new set of challenges and character development for him.
One possible plotline could be that Harry Potter has a split personality like Two - Face. Maybe in some situations, his 'good' side tries to uphold the values of Hogwarts and fight against the Dark Arts, while his 'bad' side is tempted by the power that Voldemort once offered. For example, when faced with a difficult decision about using a powerful but dangerous spell, his two sides battle it out internally.
In some fanfictions, the Horntail and Harry might have a telepathic connection. This allows Harry to understand the dragon's thoughts and motives, and they work together to uncover secrets in the wizarding world. For example, they might find a hidden chamber that holds a powerful magic item that could change the course of the war against Voldemort.
One possible plotline could be Harry using his Sans powers to avoid danger in the wizarding world. For example, he might use teleportation abilities similar to Sans to quickly escape from Death Eaters. Another could be him using his powers in Hogwarts challenges, like getting through mazes or solving puzzles with his special skills.
One interesting plotline could be the little sister discovering she has her own unique magical abilities that are different from Harry's. For example, she might be able to communicate with magical creatures in a way no one else can.
One possible plotline could be Harry having to find creative ways to get by without money. For example, he might barter his magical skills for goods and services. He could offer to help with spellcasting in exchange for food or school supplies.
One possible plotline could be the discovery of the secret child and how it affects Harry's relationships with his friends and family. For example, Hermione and Ron might be shocked at first but then become supportive. Another could be the challenges the child faces growing up in the wizarding world with this secret hanging over them.
One possible plotline could be Harry using his shadow clones to outwit Voldemort. For example, he could send the clones to different locations to mislead the Death Eaters while he sneaks into a secret lair to find a powerful artifact to defeat Voldemort.
One common plotline is the daughter inheriting Harry's magical abilities in a unique way. For example, she might be able to communicate with magical creatures on a deeper level than Harry ever could. Another plot could be about her facing a new dark threat at Hogwarts, using her father's fame both as an advantage and a burden. She could also go on a journey to discover a long - lost magical artifact that Harry was somehow connected to in his past adventures.