One great 'Harry Potter Takes Control' fanfiction is 'The Power Within Harry' which shows Harry taking control of his destiny in a unique way. It has him making decisions that are different from the original story, like taking charge of his magical training earlier.
Well, it could be about Harry Potter having a kind heart and taking in various 'strays' in the wizarding world. Maybe he takes in lonely or lost magical creatures, or perhaps other students who don't really have a place to belong. It might explore his nurturing side and how these 'strays' change his life or the Hogwarts environment.
In this fanfiction, it could be that Harry takes over the House of Potter to restore its former glory. He might have to deal with dark forces that have been lurking around the property, and he uses his skills and the help of his friends to cleanse it. Maybe he uncovers a plot against the wizarding world that was somehow connected to his family's house, and he has to prevent it from coming to fruition.
In this fanfiction, Harry might go to a magical beach. He could enjoy sunbathing while his magic keeps the sun from burning him. He might also meet some new magical creatures that only come out during holidays.
Some of the younger students who looked up to Harry, like Neville, could support him. Neville has grown to be a strong and brave character. He might see Harry's actions as a way to make the wizarding world a better place. Also, those students who have felt wronged by Dumbledore's decisions in the past, perhaps in terms of school policies or safety, could come forward to support Harry in the court case.
He becomes more nurturing. Taking care of a baby forces him to be gentle and patient, which are new traits for him. He might also become more responsible as he has a new life to look after.
There could be some antagonists as well. Maybe some dark wizards who were enemies of the Potter family in the past and are still lurking around the house, trying to stop Harry from taking full control. There might also be some Ministry of Magic officials who are interested in the House of Potter for various reasons, such as the possible presence of powerful magic items. And Neville Longbottom could also be involved, as he was a key figure in the fight against Voldemort and could be there to support Harry in this new adventure.
Well, Harry might use his magic to make the baby laugh. For example, he could turn the baby's rattle into a little magical creature that dances around. He'd probably also be very protective, like how he was with his friends at Hogwarts.
If Harry Potter takes a heritage test in fanfiction, it could be a very interesting development. Firstly, the test could show that he has a more complex bloodline than he initially thought. It might uncover that there are elements of his heritage from other magical cultures, not just the British wizarding world. This could open up new storylines where he has to deal with different magical traditions and powers related to his newly - discovered heritage. Secondly, it could also shed light on the reasons behind some of the strange things that have happened to him throughout his life, as they could be related to his hidden heritage. And finally, it could lead to him forming new alliances or facing new enemies based on what the heritage test reveals.