One possible plot could be that the puppy is a key to a hidden treasure. Harry has to follow the puppy's instincts to find the treasure which could be something very important for the wizarding world. Another plot could be that the puppy is in danger from a dark wizard who wants to use it for some evil experiment, so Harry has to protect it at all costs.
The puppy could be a symbol of hope in a dark time for the wizarding world. Harry finds the puppy during a difficult period, and as he nurtures it, it starts to bring positive changes to the people around him. People are drawn to the puppy's innocence and it gives them the strength to fight against the encroaching darkness. This plot could explore themes of hope, love, and the power of small things to make a big difference.
A plot might involve the puppy being a magical hybrid. Harry discovers that the puppy has the powers of both a normal dog and a magical creature. As he tries to understand these powers, he gets into all sorts of adventures. Maybe the puppy can communicate with other magical animals, and Harry uses this ability to solve a mystery in the Forbidden Forest.
Perhaps it's a story where Harry is born with cat ears due to some strange magic in his family's past. He could be an outcast because of it at first, but then he discovers that his cat ears are actually a sign of a special power. This power could be related to communicating with magical creatures, especially cats, which then helps him in his adventures. He might use this newfound ability to gather information or even form an army of magical cats to fight against the dark forces.
One possible plot is that the puppy was abandoned in the basement by its previous owner. It had to struggle to survive with little food and water until someone discovered it.
Well, one possible plot could be that Harry's friends race against time to find an antidote. Maybe Hermione uses her vast knowledge of magic to research ancient spells and potions that could counteract the poison. Another could be that the poison has some strange side - effects on Harry, like giving him temporary new magical abilities while also slowly killing him, and he has to figure out how to use these new powers to save himself. Or perhaps the poisoning is part of a bigger conspiracy within the wizarding world, and Harry's poisoning is just the first step in a plot to take over Hogwarts or the Ministry of Magic.
Well, perhaps the plot could involve Harry being raised as a Malfoy heir. He would be taught the pure - blood ideology from a young age. But as he goes to Hogwarts, he starts to question these beliefs. There could also be a plot where Lucius has some hidden motive for having Harry as his son, like using Harry's connection to Voldemort for his own gain. And Harry has to figure out his place in this web of lies and power plays.
One possible plot could be that Fleur betrays Harry in a Triwizard Tournament - related task, perhaps by secretly helping the other champions. Another might be that Harry discovers Fleur has been passing information about the Order of the Phoenix to the wrong side. Maybe Fleur betrays Harry's trust regarding a personal secret, like his feelings for Ginny, and uses it to her advantage in some way.
In this 'harry hates himself fanfiction', a plot could involve Harry being framed for a crime he didn't commit. Everyone at Hogwarts turns against him, and he starts to believe that he must be a bad person if so many people think he's guilty. So he begins to hate himself. Also, it could be related to his relationship with Voldemort. If he starts to see similarities between himself and Voldemort in terms of power or ambition, that could drive him to self - hatred. Another idea is that he fails an important mission and blames himself so much that it turns into self - hatred.
One possible plot could be that Harry has been kidnapped by a dark wizard who wants to use his powers for evil. Another could be that he has run away to find a way to defeat Voldemort on his own without endangering his friends. Maybe he's lost in a mysterious magical realm while on a quest and can't find his way back.
One possible plot could be that Harry finally snaps after years of abuse from the Dursleys. He might discover some dark magic that he uses against them in a fit of rage. Maybe he finds out they were involved in something really evil that endangered his life all along, and that's what drives him to murder them.
One possible plot could be that they disappear to a parallel magical dimension. In this dimension, they have to learn new forms of magic to survive and find their way back home. Maybe they encounter strange magical creatures that are unknown in their own world.
One possible plot could be that everyone believes false rumors about Harry being a dark wizard. His friends from Hogwarts, including Ron and Hermione, turn their backs on him. Harry then has to find a way to prove his innocence all alone, perhaps by going into hiding and secretly investigating who spread the lies.