The settings can merge as well. Picture a scenario where Hogwarts is under attack and the Shadowhunters come to help. The ancient halls of Hogwarts filled with Shadowhunters using their unique weapons and magic would be an amazing sight. The fanfic authors can use these elements to create new and exciting storylines that draw on the best of both worlds.
In fanfic, they can blend in various ways. For example, the magic systems can be combined. The runes from 'Mortal Instruments' might be used alongside spells from 'Harry Potter'.
I really like 'Crossing Realms: Mortal Instruments in Hogwarts'. It takes the characters from the Mortal Instruments series and drops them into the world of Harry Potter. It shows how they adapt to the new magical environment, for example, Jace trying to understand Quidditch while also dealing with the threats in Hogwarts that are different from those in his own world.
Well, some fanfics blend the two worlds by making 5sos be related to some wizarding families. So, they already have a connection to the wizarding world without really knowing it. Then, as they discover their heritage, they get involved in the Harry Potter storylines. It could be that one of the 5sos members has a long - lost wizard relative and that's how they are drawn into the magical universe. This way, the two worlds are intertwined in a more family - based way.
Well, first of all, the wands in Harry Potter could have an interesting interaction with the vampiric powers. A wizard could use a spell from their wand to create a shield against a vampire's attack. And the potions in Harry Potter could be used to either cure someone who is turning into a vampire or to enhance a vampire's abilities in some strange way. The magical creatures in both worlds could also play a role. Thestrals, which are associated with death in Harry Potter, might have some connection to the vampires in Dracula Untold since vampires are undead. The fanfic could explore these connections and create a whole new set of magical rules.
In harem fanfictions, the magic of 'Harry Potter' often interacts with the vampiric nature of 'Vampire Diaries'. For example, the wizards might use spells to protect themselves from vampires or to understand their powers better. The Hogwarts houses could also play a role, like Slytherins being more interested in the power of vampires. The harem aspect comes in when characters from both worlds are attracted to the main character, who might be a wizard or a human with special abilities.
Well, in these fanfictions, the magical creatures in Harry Potter can be compared or even interact with Pokémon. The Hippogriff, for example, could be seen as a more magical version of a flying Pokémon. And the concept of magical potions could be used to create something that affects Pokémon in different ways, like a potion that makes a Pokémon stronger or more docile. The Portkey in Harry Potter could also be used to transport trainers and their Pokémon to different magical locations in the wizarding world.
The themes blend by pitting the light - hearted and somewhat familiar magic of Harry Potter against the mind - bending, incomprehensible horror of Cthulhu. For instance, the concept of good vs. evil in Harry Potter takes on a new dimension when faced with the amorality of Cthulhu - like beings. The wizards' sense of order and their magical laws are challenged when these chaotic and eldritch forces enter their world.
Well, in some fanfics, the honor code of the Yautja might blend with the Gryffindor's sense of bravery. A Yautja might respect a Gryffindor who shows great courage in the face of danger, just as they respect worthy opponents in their own culture.
The worlds might blend through the use of shared magical elements. For instance, both have magical creatures. The gargoyles' ability to turn to stone during the day and come alive at night could be related to some form of Transfiguration magic in the Harry Potter world.
Sorry, I have no clue. It's possible that Mortal Instruments isn't a fanfic of anything and stands on its own as an independent work of fiction.
Well, in some fanfictions, the magic can be used to enhance the weapons in Team Fortress 2. For example, a spell could be cast on a sniper rifle to make it more accurate. Or the wizards could use magic to create barriers like the ones in Team Fortress 2 maps.