Well, it could be a really wacky plot. Maybe the Jackass crew somehow gets transported into the Harry Potter world. They could be causing chaos in Hogwarts, like trying to do their crazy stunts on the moving staircases and freaking out the students. They might even try to use magic items in their stunts, not really understanding the power and danger of them.
The characters would interact in very strange ways. The Hogwarts students would be shocked by the Jackass crew's behavior. The Gryffindors might be initially intrigued, while the Slytherins would be disdainful. Harry and his friends would probably try to keep the Jackass guys out of trouble, but it would be difficult as they are always looking for the next wild thing to do.
First, decide on the main plot. Will it be more focused on the Harry Potter side with a touch of Jackass humor, or vice versa? For example, if you want it to be more Harry Potter - centric, you could start with a normal Hogwarts day and then introduce the Jackass - like chaos.
There could be a fanfic where the Harry Potter characters are forced to participate in Jackass - like challenges. For example, Ron might be challenged to eat a really disgusting magical creature - based food item, similar to the gross - out challenges in Jackass. This would be a really unique and humorous take on the two universes combined.
The fanfic could center around Harry's life outside of the main events of the books. For example, it could explore his summer holidays in more detail. He could be spending time in the Muggle world and using his magic in creative ways to solve normal, everyday problems. He might use magic to help his neighbor fix a broken fence without the neighbor realizing it was magic. This would add a new dimension to his character and show how he can adapt his magical abilities to different situations.
One possible plot could be that Harry Potter is hired by Sherlock Holmes to help with a case that involves dark magic. Harry uses his knowledge of the wizarding world to uncover clues that Sherlock couldn't find with just his deductive skills.
Imagine Harry Potter as a bartender. He could be using his skills not just in mixing drinks but also in reading people. Since he has faced so many challenges in his life, he can easily spot if a customer is hiding something or if they are in trouble. His bar could become a place where secrets are shared, and he has to use his wits and magic to keep things in order. He might also have to deal with rival bartenders from other wizarding establishments who are jealous of his popularity and unique drinks.
The plot could involve Harry Potter discovering he has some sort of connection to a dragoness. Maybe he can communicate with her telepathically. They could team up to fight against dark forces in the wizarding world. For example, Voldemort might be after the dragoness for her powerful magic, and Harry has to protect her while also using her strength to defeat Voldemort.
One possible plot could be a deaf Muggle - born student getting their Hogwarts letter. They face difficulties in the beginning as they can't hear the instructions well. But they soon discover a magical device that helps them 'hear' in a magical way, like through vibrations that translate into words in their mind. Then they go on to prove themselves in classes like Charms and Potions, making friends along the way.
Well, it could be that Harry discovers a hidden chamber in Hogwarts that has Xenomorphs in it. Maybe he has to use his magic to fight them off or find a way to co - exist.
Well, perhaps the Hitman gets transported into the Harry Potter universe by some sort of magic accident. He then uses his combat and assassination expertise to help Harry Potter and his friends in their fight against Voldemort. He could teach them some non - magical ways of combat and they could teach him about magic in return. This would create an interesting dynamic between the Muggle - like Hitman and the magical characters.