In this kind of fanfiction, perhaps a group of young wizards are exploring the concept of Animagus transformation when they accidentally open a portal to a realm related to Cthulhu. They then have to use their Animagus forms in unexpected ways to survive and close the portal. Their Animagus forms might start to take on some Cthulhu - like features as they are exposed to the strange energy from that realm. This could lead to a lot of internal struggle as they try to keep their sanity and their wizarding identity while dealing with these new and terrifying changes.
A possible plot in such a fanfiction could be that a dark wizard discovers the existence of Cthulhu through some ancient and forbidden magic. He then tries to use Animagus forms to channel Cthulhu's power. This would likely cause chaos in the wizarding world as the power of Cthulhu is not meant to be tampered with. Other characters in the story, like Harry Potter and his friends, would have to figure out how to stop this dark wizard before the world is plunged into a nightmarish state.
Well, if Harry Potter becomes a Phoenix Animagus in fanfiction, he would gain some really cool abilities. For example, he could regenerate from ashes like a phoenix. He might also have the power of flight, which would be a huge advantage in battles or just for getting around quickly. His connection to magic could become even stronger as the phoenix is a very magical creature. And he could use his new form to spy on the Death Eaters without being detected easily.
If Harry were a Dragon Animagus in the First Task, it would change the whole dynamic. He could use his dragon form to create a diversion. For example, he could make the real dragon chase him away from the egg, and then quickly transform back and snatch the egg. Also, his dragon form might have some special abilities like breathing fire in a controlled way to fend off the real dragon if it attacks.
One possibility is that it could communicate with the characters in a different way. If it was a cat like Crookshanks, it could use its human form to convey important information that it couldn't as a cat. Maybe it has seen something in the wizarding world that only an Animagus could understand and needs to tell Hermione and her friends.
Dumbledore could be his mentor. He has vast knowledge and experience, and he would likely see the potential in Harry being an Animagus. He could guide Harry through the difficult process of learning to control his transformation and use his Animagus form for good.
Another possibility is that he becomes a fox. Foxes are clever and sly, which are qualities that Harry has developed over the years. As a fox, he could use his wits to outsmart his opponents. He could also easily blend into the forest environment, which would be handy for hiding or sneaking around.
One plot could be that a group of dark wizards are trying to use the magic of extinct Animagus for evil purposes. A group of Hogwarts students learn of this and embark on a quest to stop them. Along the way, they learn about the history of the extinct Animagus forms and how to counter the dark magic being used. This would involve a lot of adventure, mystery, and the students using their own magic skills and knowledge of the wizarding world.
One possible plot could be that the crocodile animagus is a new student at Hogwarts who has to hide their form at first because they are afraid of being bullied. But then they use their crocodile abilities to save the school from a dark wizard attack.
In 'Harry Potter' fanfiction, a shark Animagus can be quite significant. It can add a new layer of danger and excitement. Sharks are known for their speed and aggression. A character as a shark Animagus could use these traits to their advantage. For instance, they could quickly swim to rescue someone in danger in a large body of water. Moreover, it could be a way to explore different cultures within the wizarding world. Maybe the shark Animagus has a connection to a group of wizards who are more attuned to the sea and its magic.
Well, in a 'Harry Potter is a Shriker Animagus' fanfiction, the plot could start with Harry having strange dreams or experiences that lead him to discover his Animagus form is that of a Shriker. As he tries to understand this new aspect of himself, he realizes that there are ancient prophecies or secrets related to Shrikers in the wizarding world. He then embarks on a journey to uncover these secrets. Along the journey, he meets other Animagi who either help or hinder him. His friends, like Hermione and Ron, might be skeptical at first but then come to accept and even admire his unique form. And he might use his Shriker abilities, such as its natural stealth or some special powers associated with it, to fight against Voldemort and his followers in ways that the original Harry Potter in the books couldn't.