Angel Dust would be a bit of a wild card. His flamboyant personality and his own set of skills (like his combat abilities) could get him into all sorts of trouble and also some interesting situations. He might befriend the Weasley twins, getting involved in their pranks but also teaching them a thing or two about his own brand of chaos. Husk, on the other hand, would likely just try to find a quiet corner in the Hogwarts library or the Three Broomsticks and avoid most of the hubbub, but would be dragged into things against his will from time to time.
Alastor would be a very interesting addition. His radio - like powers could potentially disrupt the magic in Hogwarts, or he could use it to his advantage, like broadcasting his own version of 'lessons' to the students. He would probably be seen as a very powerful and somewhat menacing figure by the Hogwarts faculty. The Hogwarts ghosts would be both fascinated and a bit intimidated by him, as he's not like any spirit they've encountered before. And his presence would surely stir up some drama and mystery in the halls of Hogwarts.
The characters from Hotel Transylvania could be new students at Hogwarts. Dracula could be a teacher of some sort, perhaps teaching about dark creatures in a different way than Hagrid. His bat form could be mistaken for a dark omen by some students at first.
Harry could be seen as a strange but powerful being. His Gryffindor courage would be respected in Asgard. Hermione might be seen as a great scholar, like the Asgardian mages. Ron could be the loyal friend who has to adapt to the grandeur of Asgard.
The Hogwarts professors could also play important roles. Dumbledore could be seen as a wise old figure, much like Rafiki. He could offer guidance to the animals and the Harry Potter characters alike. Snape, on the other hand, might be a bit more difficult to place, but perhaps he could be a sort of protector in the shadows, using his potions knowledge to help heal any injured animals or deal with magical threats in the Pride Lands.
Neville Longbottom could befriend Mia in fanfiction. Neville, with his new - found confidence in the later Harry Potter books, could teach Mia about being brave and standing up for herself. He could also share his knowledge of plants, and they could start a garden together in the Genovian palace grounds. This would not only be a cute friendship but also a way to blend the two different worlds of the two series.
Naruto would probably be very curious about the characters in the Hazbin Hotel. He might befriend Charlie right away because of her kind - hearted nature. He would be confused by some of the more devious characters like Alastor, but would likely respect their power. The Hazbin Hotel characters, on the other hand, would be intrigued by Naruto's bright orange jumpsuit and his ninja abilities. They might ask him to show off his jutsu.
The characters from 'Shameless' are known for their scrappy and street - smart nature. In the 'Harry Potter' world, they could be Muggles who accidentally discover the wizarding world. For example, Carl could be exploring an old abandoned building and find a hidden passage to Diagon Alley. Or they could be Squibs related to some important wizarding families. Like Veronica could be a Squib who has always felt out of place in the Muggle world and finally finds a sense of belonging in the wizarding world's fringes.
Harry Potter himself could be seen as a kind of foreign wizard in the RWBY world. He might be initially confused by the concept of Dust but quickly adapt and use his magic to enhance the RWBY team's capabilities. Hermione would probably be fascinated by the study of Dust and Semblances, and use her vast knowledge to help bridge the gap between the two magic systems. Ron could be the one who forms quick friendships with the RWBY characters, sharing his sense of humor and loyalty.
The characters could be trainers. Harry, for example, could start his Pokemon journey in a region similar to Kanto. He might choose a Charmander as his first Pokemon, just like how he was drawn to the Firebolt in the original series. Ron could be more interested in food - related Pokemon like Snorlax. Hermione would be the type to research every single Pokemon and their abilities thoroughly before choosing her team. They could use their magic skills in a different way, like using spells to communicate with Pokemon or to enhance their Pokeballs.
Well, Harry could be the Beast. He has that scar which could be seen as a mark of his 'beastliness' in a way. And Hermione could be like Belle, intelligent and curious, and she might be the one to see past Harry's outward appearance (the scar and the effects of the curse) and fall in love with him for who he really is.
Well, he could be a foreign exchange student of sorts from a hidden land of ninjas. His skills would make him stand out immediately. He might befriend Harry and help him train in a different way of combat, using his Sharingan to analyze the weaknesses of their enemies like Death Eaters.