One major difference is that fanfiction can take dark creatures in unexpected directions. For instance, the Nundu could be a tamed creature in some fanfics, used by a wizard for protection instead of being just a wild and dangerous beast as in the books. The Grindylows might be shown to have a culture of their own in fanfiction, with their own laws and traditions. In the original, they are more of a basic threat in the water. Fanfiction also allows for the creation of new hybrids of dark creatures, which is something that doesn't exist in the original Harry Potter universe.
In the original books, the creatures have well - defined characteristics set by J.K. Rowling. But in fanfiction, they can be drastically altered. For example, the werewolves in the books are mainly seen as dangerous during full moons. In fanfiction, a werewolf might be able to control their transformation at will and be a more complex character, perhaps even a hero. So the nature of the creatures can be completely reimagined in fanfiction.
In fanfiction, magical creatures often have more complex personalities. For example, in the books, the Blast - Ended Skrewt is mainly just a strange and dangerous creature. But in fanfiction, it could be given a backstory that makes it more sympathetic. Also, new abilities might be added. The Thestral might be able to communicate telepathically in some fanfictions, which is not in the original books. And sometimes, the relationships between magical creatures and characters are explored more deeply in fanfiction.
In the original Harry Potter series, creatures like the Dementors have a specific origin and role. However, in fanfics, we might see Dementors being controlled by a new kind of magic or even having different powers. Some fanfics might make Dementors be able to transform into other forms, which is quite different from what we know in the books. This is because fanfic authors want to explore new storylines and add twists to the familiar Potter world. They can take a well - known creature and give it new abilities or backstories to fit their own creative vision for the story.
In fanfic, magical creatures may have different behaviors compared to the original books. For example, a Thestral in fanfic might be more social towards certain characters than in the books. Also, their appearances could be altered. A Hippogriff in a fanfic could have a different color or pattern on its feathers. And sometimes, new abilities are given to them. Maybe an Occamy in fanfic can communicate telepathically which it can't do in the original.
Werewolves are also a popular dark creature in fanfiction. Writers may explore their relationships with other characters in more depth, like how they interact with Hogwarts students. For example, a werewolf character could be a misunderstood outcast trying to find his place.
In fanfiction, dark creatures can be more sympathetic. For instance, a vampire might be shown as a victim of his own condition rather than just a menacing figure. This gives readers a new perspective on these usually feared beings.
In fanfiction, Bubotubers might have enhanced abilities. For instance, they could be made to move around more actively compared to the rather stationary ones in the books.
The weapons in the original Harry Potter books are mostly traditional magical items like wands, swords (like Godric Gryffindor's sword), and potions which can be used in a sort of weapon - like way. However, fanfiction weapons are often much more elaborate. Fanfiction might introduce things like a ring that can teleport the wearer anywhere in Hogwarts or a necklace that gives the user the power to control the weather. These weapons are not bound by the limitations of the original book's lore as strictly, so they can be more creative and extreme in their capabilities.
Fanfiction often gives boggarts more abilities or different rules. In the original books, the Riddikulus spell was a fairly straightforward way to deal with them. But in fanfic, boggarts might be harder to defeat, perhaps requiring a combination of spells or a deeper understanding of one's own psyche. They could also have the ability to influence the environment in different ways, like creating illusions that are more difficult to distinguish from reality.
Some dark creatures could have magical powers that are not fully understood. They could create barriers or illusions to hide Harry from his pursuers. In the fanfiction, they may also use their knowledge of the dark arts in a positive way to counter the dark magic aimed at Harry. They might be able to sense danger before it arrives and take preemptive action to keep Harry safe.