Perhaps a new dark wizard or witch who is jealous of Amelia Bones' power and influence in the Ministry. They might see Harry as a way to get to Bones, by either using him as a pawn or by trying to turn him against her. This new antagonist could have a unique and dangerous brand of dark magic that challenges both Harry and Amelia.
There could be a group of dark wizards who are working together to bring chaos to the wizarding world. They target Amelia Bones because of her position in the Ministry and Harry Potter because of his fame. This group, with their evil intentions and powerful dark magic, would serve as the main antagonists in the fanfiction.
A power - hungry wizard within the Ministry itself could be the antagonist. He sees Amelia Bones as a threat to his rise in power and also dislikes Harry for his influence among the wizarding community. He spreads false rumors about them and tries to get them in trouble, all while trying to further his own political agenda.
It could be a dark wizard who has infiltrated the Ministry of Magic. This antagonist might be trying to undermine Amelia Bones' work and also target Harry for his fame and power.
The obvious antagonists would be the Death Eaters. They are always up for causing chaos and harm. If Voldemort has a particular interest in Amelia Bones, perhaps because of her knowledge or position in the wizarding world, he would send his loyal Death Eaters to capture her. Another possibility could be some rogue dark wizards who are trying to gain power and see Amelia as an obstacle.
It could be some of the remaining Death Eaters. They might target Amelia Bones because she is a powerful and important figure in the Ministry of Magic. Her knowledge and influence could be a threat to their plans of resurrecting Voldemort's ideology or causing more chaos in the wizarding world.
Amelia Bones is a high - ranking official in the Ministry. She is part of the wizarding establishment that Harry Potter often has to interact with. Her role could be crucial in times of upheaval, like during the return of Voldemort. She might offer her expertise or resources to Harry and his friends in their fight against the Dark Lord.
There isn't really one 'best' author as different readers have different tastes. However, some authors who have a large following for their 'Harry Potter' fanfictions might also do a great job with Amelia Bones. They usually have a good understanding of the overall 'Harry Potter' universe and can integrate Amelia Bones into the story in a seamless way. You might want to look for authors who have received a lot of positive reviews for their stories involving similar themes or characters.
They could have a mentor - mentee relationship. Amelia, being older and more experienced, could guide Harry in his fight against the dark side.
One possible plot could be that they meet during an investigation into dark magic. Harry, with his experience, and Amelia, as a powerful figure in the Ministry, start to respect and then fall for each other. As they work together, they face challenges from dark wizards who try to stop their investigation and their relationship.
In a 'Harry Potter rescues Amelia Bones' fanfiction, perhaps Amelia Bones is captured by Death Eaters. Harry, using his skills and courage, manages to infiltrate their lair. He could use the Invisibility Cloak and his Patronus to fend off Dementors guarding her. With his wand at the ready, he overcomes the dark magic spells set by the Death Eaters and frees Amelia Bones. Then they escape together, and Amelia might provide some crucial information about Voldemort's plans to Harry.