A 'Harry Potter train's alone' fanfiction could have a plot where the train is abducted by a powerful dark force. The train has to fight back using its own magical properties. It could call on the spirits of the railway tracks or the magic of the surrounding forests to help it. Or perhaps the train discovers that it has a long - lost sibling in the form of another magical vehicle, and it goes on a quest to find it while being alone.
In a fanfiction about the Harry Potter train being alone, perhaps it could become a magical entity on its own. It might start to travel to mysterious destinations not on the regular Hogwarts route. Maybe it would pick up lost magical creatures or even lost wizards from different eras. It could be a place of refuge for those in need, with its compartments transforming into mini - magical habitats.
In some 'peter is alone fanfiction', he could be alone in a strange new place. For instance, he's transported to a different dimension where he doesn't know anyone. He has to adapt, survive, and maybe find a way back home all by himself. This kind of plot can explore his character growth, his resourcefulness, and how he deals with the isolation in a completely unfamiliar environment.
Maybe he's frustrated with all the prophecies and his role in the fight against Voldemort. He doesn't want to be constantly pushed into being the hero. He might want some time to figure out who he really is outside of all these expectations. Also, he could be feeling a bit overwhelmed with his studies and the extra - curricular activities like being in Dumbledore's Army. All these things together make him long for some solitude.
Well, one possible plot could be a wizard who has picked up the Muggle habit of smoking cigarettes and how it affects his magic. Maybe his spells start to go awry because the smoke interferes with the magical energy. Another could be a group of Hogwarts students who discover cigarettes in the Forbidden Forest and have to deal with the consequences of this Muggle item in a magical place. But these are just very speculative ideas as it's not a common type of fanfiction.
Perhaps there's a fanfiction where Ron is forced to work at a dentist's office as a punishment. He has to deal with all kinds of strange patients, from veelas with very sharp teeth to giants with massive molars. His misadventures in the dentist office, trying to use magic to get out of his work or accidentally making things worse, could make for a really funny and engaging plot.
One possible plot could be that Harry inherits the Doctor's time - traveling abilities. He could use them to go back in time and prevent some of the tragedies in the Harry Potter world, like the death of his parents. Another plot could be that the Doctor's enemies target Harry, thinking they can use him to get to the Doctor. And Harry has to learn about his true heritage and how to use his new - found powers to fight back.
One possible plot could be that Hermione accidentally casts a spell on Harry during one of their Hogwarts adventures, turning him into a pet. She then has to take care of him while trying to find a way to reverse the spell. Along the way, they encounter various challenges and have to rely on their friendship to get through.
One possible plot could be Harry trying to understand Voldemort's past and motives through the letters. Maybe he writes to ask about Voldemort's childhood, what led him to become so evil. Another could be Harry attempting to persuade Voldemort to change his ways, using the letters as a form of communication to reach the dark wizard's humanity. Or perhaps Harry writes to taunt Voldemort, using the fanfiction as a way to get under his skin and make him angry in a psychological battle.
A possible plot could be that the dragon is a new, unknown and extremely powerful species. Harry is sent to investigate it but underestimates its power and gets killed.
One possible plot is that Harry discovers a hidden prophecy that says only by helping Voldemort can he truly save the wizarding world in the long run. So, he reluctantly starts to assist Voldemort in his conquests, all while secretly planning to turn the tables.