A sucubus familiar could be a magical being from a far - off and dark corner of the wizarding world. It could be that a powerful and unorthodox wizard has managed to bind it as a familiar. In the Harry Potter universe, it might be seen as a very dangerous and controversial choice. For example, Dumbledore might be extremely cautious about it, while some dark wizards might be envious and try to steal it.
A Quetzalcoatl as a familiar in the 'Harry Potter' fanfiction universe would bring in a whole new cultural aspect. The creature has strong ties to Mesoamerican mythology. It could interact with the magic of Hogwarts in interesting ways. For example, its connection to the sun in its native mythology might translate into some sort of light - based magic within the 'Harry Potter' context. It could also have a special bond with Harry that goes beyond the normal familiar - wizard relationship, perhaps due to its more ancient and powerful nature.
One possible plot could be a young wizard accidentally summons a sucubus as a familiar. The sucubus, instead of being purely malevolent, has her own motives and secrets. She could help the wizard in his adventures at Hogwarts while also causing some chaos due to her nature. For example, she might use her charm to get out of tricky situations or to get information from other students or teachers, but this also gets the wizard into some trouble with the school authorities.
A nekomata could fit in as a rare and powerful familiar. It could be from a far - off magical land and brought to Hogwarts by accident or on purpose. For example, it might have been smuggled in by a dark wizard initially but then escapes and finds Harry.
Hawkgirl could be a new kind of magical creature. Her ability to fly with her wings would be a unique form of magic in the wizarding world. She might be a protector of some hidden magical place in Hogwarts or the Forbidden Forest, like a guardian of an ancient magic that Voldemort is after.
In fanfiction, umbramancy can fit in by being a long - lost or forgotten magic. It could be something that was once used by ancient wizards but lost over time. For example, it might be rediscovered in the Forbidden Forest by a curious student.
Shukaku could be a powerful magical beast that has been sleeping deep within the grounds of Hogwarts for centuries. Only a very powerful spell or a unique combination of spells could awaken it. Once awakened, it could either be a great ally or a terrifying foe depending on how the wizarding community treats it.
Supergirl could be a foreign exchange student of sorts in the Harry Potter universe. She could be there to study magic while also sharing her own Kryptonian knowledge. Her superpowers would make her stand out, but she would also have to learn the rules of the wizarding world, like not using her powers when it's against the wizarding code.
He could fit in as a unique hero. His magic could be seen as a special power like the others in DC. For instance, he could use his Patronus charm to fight off fear - inducing villains.
Illumi can fit in as an outsider with unique skills. His combat and stealth abilities are not like anything in the wizarding world, so he could be a wildcard. For instance, in some fanfictions, he might be seen as a new kind of threat or an unexpected ally to the Order of the Phoenix.
Freerunning can fit into the Harry Potter universe by adding a new dimension to movement. For example, it can be used for escaping from dark wizards in the narrow alleys of Diagon Alley or Hogsmeade. The characters can use their parkour skills to quickly jump over obstacles and get to safety.