Some fanfictions might depict the Green Goblin as a visitor from another dimension. When he arrives in the Harry Potter universe, he starts to learn magic and uses his knowledge from his own world to make unique combinations. For example, he could combine his flying technology with a broomstick to create a super - fast flying device.
In fanfiction, the Green Goblin might be a creation of a dark wizard's experiment gone wrong. This would link his origin to the magic in the Harry Potter world. His appearance could disrupt the balance between good and evil in the wizarding world as he has his own motives and methods that are different from the typical wizards and witches.
Mithril might be incorporated into the fanfiction as a material that has a special connection to certain magical creatures. Maybe unicorns are attracted to Mithril, and a plot could revolve around a group of students trying to use Mithril to lure a unicorn to safety from a poacher. Along the way, they learn more about the magical properties of Mithril and how it interacts with the magic of the unicorn, which in turn could have implications for other areas of magic within the 'Harry Potter' universe.
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.
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.
Well, in fanfiction, Merlin might be reincarnated in the Harry Potter era. He could retain some of his past memories and powers. As a character, he would bring a different style of magic, one that is more in tune with nature and less structured compared to what the wizards in Harry's world are used to. His arrival could cause a stir among the magical community, with some seeing him as a savior and others as a threat, all while having a special connection with Harry, perhaps as a mentor or a long - lost relative in the magical sense.
Well, in fanfiction, the changling can add an element of mystery. It can be seen as a creature that blurs the lines between the known magical beings in the Harry Potter world. For example, it could be a being that can shift forms like a Metamorphmagus but with different rules and limitations.
Russian royalty can add a new layer of mystery. They might have had their own unique brand of magic that was different from what Harry was used to in the UK. For instance, their magic could be more closely tied to nature, like the freezing winters of Russia.
An amputee character can bring a new perspective. They can use magic to create prostheses or aids. For example, they might use a spell to make a magical limb that can do things normal prostheses can't. This adds a unique element to the magical world.
The Tesseract in Harry Potter fanfiction can be seen as a link between different dimensions in the wizarding world. It could be the key to unlocking secrets about the origin of magic. For example, it might be that the founders of Hogwarts knew about the Tesseract and used its power to build certain parts of the school. Or, it could be that the Tesseract has the ability to break the boundaries between the Muggle world and the wizarding world, creating a whole new set of challenges and adventures for the characters.
He might be a character who was involved in the politics of the wizarding world. Fanfiction could explore how his influence, either positive or negative, affected the balance of power. And this could in turn impact the events that Harry has to face. For example, if Arcturus Black had made certain alliances, it could change the dynamics of the war against Voldemort.
Alien tech can fit into the Harry Potter universe in fanfiction by being a source of mystery and power. Imagine an alien crystal that has the ability to amplify magic. Wizards would be intrigued by this and would try to harness its power. Also, if there are aliens with their own form of 'magic' which is really just advanced technology, they could interact with the wizards. For instance, an alien 'teleporter' could be compared to the Apparition spell in the wizarding world. The differences and similarities between the two could be explored in the fanfiction, creating interesting storylines.