They could be part of a hidden threat in the wizarding world. Maybe they were sealed away long ago and are now being accidentally released. Their presence would cause chaos as they are so different from the usual magical creatures in Harry Potter.
One way the Weeping Angels could fit is through a time - travel aspect. Since they are related to time in their own 'Doctor Who' lore, they could be brought into the Harry Potter world through a time - travel accident. This could lead to all sorts of plot twists as the characters have to deal with the time - altering effects of the Weeping Angels while also dealing with their own magical problems.
Harry would likely be very cautious. He's faced many dangerous creatures before, but the Weeping Angels are a whole new level of threat. He'd probably try to keep his friends safe while also trying to figure out how to stop them. Hermione would immediately start looking for a way to defeat them, researching in every book she could find. Ron would be on edge, ready to fight if necessary but also a bit nervous.
One great fanfiction might be one where the Weeping Angels are introduced into the Hogwarts grounds. The Weeping Angels' time - freezing abilities could create really interesting scenarios with the magic of Harry Potter. For example, they could freeze some spells in mid - air, leading to a very different kind of battle or mystery for Harry and his friends to solve.
Gwendy can fit in as a new friend to the main characters. She could join Harry, Ron and Hermione on their adventures and offer a fresh perspective. Maybe she has a different approach to solving problems, like using her knowledge of Muggle technology in a magical way.
In a fanfic, Harry Potter could enter the Avengers' story through a magical portal. Once there, he could use his magic to complement the Avengers' skills. For example, his ability to communicate with snakes could be useful if they encounter snake - like villains. His experience with horcruxes might also give him insights into dealing with powerful and hard - to - destroy enemies in the Avengers' world. His wand could be a unique weapon in their battles, and his ability to perform complex spells could turn the tide in difficult situations.
Pikachu could be a special guest at Hogwarts. It might be brought there by a powerful wizard who has traveled to other dimensions. And it could use its electric attacks to protect the school from dark forces.
Alucard could fit as a powerful outsider. His vampiric abilities like super strength, speed, and the ability to turn into mist or a bat would be very different from normal wizard magic. He could be a sort of anti - hero, helping Harry when it suits his own goals. For example, if there was a dark wizard using blood magic in a way that threatened Alucard's existence too.
It could be a really dark and strange fanfiction. Harry would likely grow up in a very different and menacing environment. The Weeping Angels' nature of being stone when observed and deadly when not could lead to a lot of tense situations for Harry.
Harry Potter himself is a likely candidate. He has shown great courage and magical ability throughout the original series. His Patronus charm, for example, could potentially be used to fend off the King of Weeping Angels, as it represents his positive energy and strength of will.
Dick Grayson could fit in as a new kind of hero in the wizarding world. He could use his detective skills, which he developed in the Batman universe, to solve magical mysteries. For example, if there were a series of strange disappearances in Hogsmeade, he could use his deductive reasoning to figure out what was going on, much like he did in Gotham.
The Dixon Brothers could be muggles who are accidentally exposed to the wizarding world. They might start out as skeptics but then become intrigued. For example, they could be neighbors of the Weasleys when they are on a mission in the non - magical world. Harry Potter could then be the one to introduce them to the wonders of magic and they could help Harry in some way, like using their street - smart skills to navigate a dangerous part of the non - magical world where a dark wizard is hiding.