One possible plot development could be that with Merlin's help, Harry discovers a new form of magic that was previously unknown. This new magic could then be used to defeat a powerful enemy.
Well, one possibility is that Merlin's friends, like Arthur, might search desperately for a cure. They could go on a dangerous quest to find a rare herb or consult a powerful sorcerer who might know how to save him. Another could be that Merlin, while poisoned, has strange visions or dreams that give him clues about his true destiny or the future of Camelot.
Merlin might use his magic skills to help Harry. For example, he could use his knowledge of ancient spells to protect Harry from dark magic. Maybe he helps Harry in battles by creating magical shields or illusions to deceive the enemies.
Perhaps in the 'harry is the heir of pendragon fanfiction', Harry's new status as the heir of Pendragon causes a stir in the wizarding world. Some might fear his new - found power, while others might see him as a great hope. He could be drawn into a political struggle within the magical community as a result.
Well, one possible plot development could be that Harry learns some really unique combat skills from Scathach. Maybe he becomes a much more formidable wizard in dueling. Another could be that he gains a different perspective on magic through her teachings, which helps him in his battles against Voldemort.
One possible plot development could be that Voldemort fully regains his power without Harry as an obstacle. The wizarding world would be plunged into complete darkness. His friends, like Hermione and Ron, might go into a deep state of despair and then form a resistance group. They would try to find other ways to defeat Voldemort, perhaps by seeking out more powerful magical artifacts or uniting with some previously neutral magical creatures.
One possible plot development could be how the wizarding world reacts to the loss of the so - called 'Chosen One' even as a baby. There might be widespread grief and fear among those who opposed Voldemort, as they had placed so many hopes on Harry. Another aspect could be how Voldemort's reign of terror continues without the threat of Harry Potter. He might become even more powerful and tyrannical, with no one to oppose him in the way Harry was prophesied to.
One possible plot development could be that his friends rally around him. They might search for rare potions or spells to heal him. For example, Hermione could be scouring the library for ancient healing magic while Ron stays by Harry's side, offering moral support.
One possible plot development could be that Harry kills Umbridge in self - defense. Maybe she attacks him first with the intent to harm or kill, and Harry has no choice but to use lethal magic in return. This would then lead to a huge uproar in the wizarding world, with some believing Harry was right and others seeing him as a murderer.
One possible plot development could be Harry's struggle with his mental health. He might experience symptoms like depression, anxiety, or post - traumatic stress disorder. Another could be his search for justice or revenge against the perpetrator. He may also face challenges in his relationships as he tries to come to terms with what happened.
One possible plot development could be that Harry discovers new magical abilities or knowledge within the Greengrass family. Maybe they have a unique magical heritage that helps him in his fight against Voldemort.