In some 'Harry Learns the Dark Arts' fanfictions, there could be a plotline where Harry uses his newfound knowledge of the Dark Arts to fight against a new, more powerful dark wizard. He might have to walk a fine line between using the Dark Arts in a 'good' way and succumbing to its evil nature. His adventures in this regard could include learning how to counteract dark spells with his own dark - art - based magic, all while trying to keep his soul intact.
One possible plotline could be Harry's internal struggle. As he learns dark magic, he has to battle his own moral compass. He might question the boundaries of good and evil. Another could be how his relationships change. His friends might be horrified or try to save him from the dark path.
One interesting plotline could be Harry discovers a hidden potion recipe that gives him the ability to communicate with magical creatures. Another might be Harry has to make a potion to save a sick friend under very difficult circumstances, like with limited ingredients.
Another plotline could involve Harry learning ancient magic related to elemental control. For example, he learns to master fire magic in an ancient way that is much more powerful than the regular spells. This newfound power helps him in battles against Voldemort's followers, as he can create massive walls of fire or send out fire - based attacks that are difficult to counter.
In this type of fanfiction, a great plotline could be that Harry stumbles upon a hidden family grimoire. Inside, he finds magic that was thought to be lost. For example, there could be spells for creating protective shields that are stronger than any known spell. Or perhaps he discovers family magic that is related to time - travel, which he then has to learn to control carefully so as not to disrupt the timeline. This discovery of family magic would add a whole new layer to his character development and his role in the wizarding world.
Obviously, Harry Potter is the main character. He is the one who is learning the Dark Arts. Then there might be his friends like Hermione Granger and Ron Weasley. They could be either supporting his new path or trying to stop him. There may also be new characters created specifically for the fanfiction, such as a secretive Dark Arts master who takes Harry under his wing.
In 'Harry Learns Alchemy' fanfic, a cool plotline might be Harry getting tutored by an old and reclusive alchemist who has secrets of the past. This alchemist could teach Harry not just about potions and transmutations but also about the history of magic through the lens of alchemy. Maybe Harry uses his new - found alchemical skills to help Ron, who has been accidentally affected by a faulty spell. He could use alchemy to reverse the spell's effects. Also, there could be a plotline where Harry enters an alchemical competition within the wizarding world and has to outwit his opponents with his unique understanding of alchemy.
One interesting plotline could be Harry's initial struggle with arithmancy concepts. He might find it difficult to understand the complex numerical magic at first, but as the story progresses, he starts to see how it relates to his overall magical abilities.
One interesting plotline could be Harry discovering a new and ancient form of magic that was lost for centuries. This could lead him on a journey to understand its origin and how to master it.
One possible plotline could be that Harry is influenced by a dark artifact. For example, he discovers a cursed object that slowly corrupts his mind, making him turn against his friends. He might start to use dark magic to achieve his goals, believing that the end justifies the means.
One possible plotline could be Ginny being influenced by a dark magical object that makes her turn against Harry. This could lead to a series of conflicts as Harry tries to figure out what's wrong with her and how to save her. Another plotline might involve Harry and Ginny being caught in a dark prophecy that forces them to make difficult choices that seem against their nature. For example, they might have to choose between saving each other or the wizarding world.