One way it could work is by having Harry Potter be a secret admirer of Gomez Addams' unique style and way of life. Maybe Harry discovers some old wizarding texts that mention a connection to the Addams family's magic. He then becomes fascinated and starts to incorporate some of Gomez's traits into his own life, creating an interesting blend of the two worlds.
In the fanfiction community, there are all kinds of out - there ideas. While the idea of 'harry potter is gomez addams fanfiction' might seem odd at first. It could potentially be a very creative and unique take. But generally, most fanfics tend to stay within the boundaries of their respective universes or do crossovers in a more expected way. So, it's probably not a big trend, but it could exist in some corner of the fanfiction world where people like to experiment with unusual combinations.
One way it could work is by having Harry Potter be transported to the world of Noctis. He could use his magic skills there and face new challenges that are different from what he's used to in Hogwarts. For example, the magic in Noctis' world might be more elemental - based, and Harry has to adapt to use his wand magic in that context.
One way it could work is if there was a magical portal that connected the wizarding world to Spider - Man's universe. Harry could accidentally stumble through it and then get involved in Spider - Man's battles, using his magic to help out.
One way could be that Godzilla somehow appears in the wizarding world. Maybe a magical experiment goes wrong and transports Godzilla there. Then the wizards and witches have to figure out how to stop it using magic.
In this fanfiction, it could be that the magic in Harry's world has a connection to the enchantment on Mjolnir. Maybe the ancient magic that runs through Harry's veins is recognized by Mjolnir's magic as something worthy. So, when Harry tries to lift it, his magic interacts with the hammer's magic in a positive way, allowing him to pick it up.
One way it could work is if Jack Sparrow somehow ends up at Hogwarts. Maybe he's chasing a magical treasure that has been hidden there. His pirate ways would clash with the strict Hogwarts rules, and Harry Potter and his friends could either befriend him or be suspicious of him. Another possibility is that Harry Potter, being a fan of Jack Sparrow, tries to model some of his actions after the pirate, much to the dismay of his teachers.
One idea could be that the Addams family visits Hogwarts. Wednesday could be intrigued by the Dark Arts classes and start causing some spooky chaos among the students. She might even try to out - do Draco Malfoy in being menacing.
A possible crossover could be in the area of magic. The Addams family might have their own brand of 'weird' magic that clashes or combines with the magic in Harry Potter. For instance, Pugsley Addams could create some really odd potions using ingredients from both the Addams' world and Hogwarts' supply.
A fanfiction could be set in a world where Hogwarts has an exchange program with Nevermore Academy (Wednesday's school). Harry Potter is chosen to go to Nevermore, and Wednesday is sent to Hogwarts. At Hogwarts, Wednesday has to deal with the magical chaos and the rather more optimistic students compared to her own schoolmates. Meanwhile, Harry has to navigate the strange and often macabre world of Nevermore, and they both learn a lot from each other's worlds.
In a fanfiction, Wednesday Addams could visit Hogwarts. She would probably find the castle fascinating, but also a bit too cheery in some parts. She might make friends with some of the darker - themed students, like those from Slytherin. And she could introduce them to her pet spiders and other creepy - crawlies. Harry would be intrigued by her and her family's attitude towards death and the afterlife, which is different from what he has learned in the wizarding world.