A great fanfiction is one where the Shadowhunters are invited to Hogwarts to teach a special class on combat using their unique weapons. It shows how the Hogwarts students react to their new teachers and their different style of magic. Another one could be about a Shadowhunter who is a secret Potterhead and has to hide his love for the Harry Potter books in the Shadowhunter society.
One interesting crossover could be the use of magic systems. For example, how would the Shadowhunter runes interact with Harry Potter's spells? Maybe a character from the Shadowhunter world could find themselves at Hogwarts and be both amazed and confused by the different forms of magic. Another aspect could be the characters' personalities clashing or working together. A brave Gryffindor and a fearless Shadowhunter might team up to fight a common evil that threatens both their worlds.
Harry Potter himself is quite popular. His status as the Boy Who Lived gives him a certain allure in the crossovers. Fans like to imagine how he would handle the different threats in the Shadowhunter world. Clary Fray is also a favorite. Her journey as a Shadowhunter, especially her discovery of her powers, can be paralleled with Harry's discovery of his wizarding abilities. And when they interact, it can lead to some really engaging storylines.
One interesting fanfiction could be about a crossover where the magic systems of both worlds collide. Maybe a Shadowhunter ends up at Hogwarts and has to adapt to the very different magical environment there. Another could involve a joint quest where characters from both universes team up to fight a common enemy, like a powerful dark wizard who has somehow gained access to the Shadow World's demons.
One interesting plot twist could be when a beloved Harry Potter character is revealed to have a hidden Shadowhunter heritage. This completely changes their identity and the way they interact with both worlds.
There are some fanfics that focus on a character from Harry Potter having a connection to a Shadowhunters' artifact. For example, Hermione might discover a hidden Shadowhunters' rune that has some sort of power related to magic in the wizarding world. This could lead to an interesting adventure where she has to team up with some Shadowhunters to figure out its purpose.
Love and relationships are also a big theme. When different universes collide in these crossovers, new love interests can be formed. It might be between a Shadowhunter and a character from another world, and this creates all kinds of drama and tension. It's not just about romantic love, but also friendship and loyalty among characters from different backgrounds. Another common theme is the fight against a common evil. Characters from different worlds might have to team up to defeat a powerful foe that threatens both of their universes.
I really like 'Mixed Realms of Blood and Magic'. This fanfiction takes the best of Vampire Academy's vampire lore and Shadowhunters' angel - demon magic system. It has a great protagonist who is trying to find her place in this combined world of vampires and shadowhunters. There are some really intense fight scenes and lots of character development throughout.
Popular malec shadowhunters fanfiction often focuses on the intense emotional connection between Alec and Magnus. It dives into their love story, highlighting their differences and how they complement each other. For example, many fics explore how Magnus' centuries - old experience contrasts with Alec's more sheltered shadowhunter upbringing, creating a rich dynamic.
In many Shadowhunters fanfictions where Alec gets hurt, it often leads to some really emotional moments. One common scenario is when he gets injured during a fight with demons. His friends and especially Magnus might be beside themselves with worry. They would do everything they could to heal him, and this could lead to some really touching interactions between the characters, like Magnus using his magic in a very desperate way to save Alec.