A plot could be that Harry is the only one who can transform into a giant wolf animagus, and he uses this form to hunt down Horcruxes in the most dangerous and inaccessible places. His wolf senses help him detect the dark magic of the Horcruxes more easily.
One idea is that Harry's giant wolf form is a result of a curse placed on the Potter family long ago. As he tries to understand this new part of himself, he discovers that there are other hidden animagus in the wizarding world who have been waiting for someone like him to appear. They guide him on how to fully use his powers as a giant wolf, and together they fight against a new dark threat emerging in the wizarding world. This plot could involve a lot of self - discovery for Harry, as well as exploring the politics and secrets of the animagus community.
A fanfiction could explore the idea that Harry Potter is a giant wolf animagus and how this affects his relationship with his friends. For example, Hermione might be both fascinated and a bit worried about this new development. Ron could be initially scared but then come to see it as another amazing aspect of Harry. The story could also involve Harry using his wolf form to communicate with other magical creatures in a way that no one else can, leading to new alliances and secrets being uncovered.
A fanfic could involve a character from Twilight who discovers they have the potential to be a wolf animagus in the Harry Potter sense. They then have to travel to the wizarding world to learn how to control this new ability. This would bring in elements of both worlds, like the magic of Hogwarts and the vampire - werewolf - human dynamic of Twilight.
One idea could be Harry discovers he's an Animagus early on, perhaps in his second year. He turns into a stag like his father and uses this form to explore the Forbidden Forest secretly. Another could be that he has to hide his Animagus form from the Ministry which is on high alert for unregistered Animagi.
One possible plot could be that Harry discovers his Animagus form as a dire wolf early on. He then uses it to secretly explore the wizarding world outside of Hogwarts, encountering new magical creatures and secrets. Along the way, he has to keep his form a secret from the Ministry of Magic who might see it as a threat.
Often, he is depicted as having enhanced senses. His sense of smell, for example, can be used to detect danger or find hidden things. His speed and agility in wolf form are also emphasized, making him a formidable presence in the Forbidden Forest or during battles.
A plot could be that a Gryffindor Animagus accidentally reveals their form during a Quidditch match. This causes chaos as everyone tries to figure out who it is. It also draws the attention of the Ministry of Magic who have strict rules about unregistered Animagi. The character then has to deal with the consequences while also trying to prove they mean no harm.
A fanfiction that stands out is 'The Hidden Dragon Animagus'. It combines the mystery of the animagus form with the power and allure of a giant dragon. The story has a slow - burn romance as well, which adds an extra layer of depth. The way the author weaves in elements from the original Harry Potter series makes it a must - read for any fanfiction lover.
One idea could be that the giant squid has a secret ability to communicate with Harry through telepathy. Another could be a story where the squid saves Harry from a dangerous underwater creature. Or perhaps a plot where the squid is actually an ancient magical guardian of Hogwarts that only reveals itself to Harry in a time of great need.
Well, an idea could be that a group of Hogwarts students discover a hidden portal that leads to the Pokemon world. There, they learn about the Pokemon's unique abilities which are somewhat similar to magic in their world. One of the students realizes they can transform into a Pokemon in the same way as an Animagus. They then bring this knowledge back to Hogwarts and start a new study group on it.
One idea could be that Harry discovers he has a strange connection to the Pokémon world. As an Animagus, he could transform into a form that has some similarities to Mewtwo, like having purple eyes or telepathic abilities. Maybe he gets transported to a world where Pokémon exist and has to use his skills as an Animagus and wizard to survive.