A new vampire who is jealous of Edward's relationship with Bella could be the antagonist. With Edward having amnesia, this new vampire could try to take advantage of the situation and win Bella over. They could also try to turn Edward into a more 'evil' version of himself while he is vulnerable.
Perhaps a group of rogue vampires who have heard about Edward's amnesia and think they can use him for their own gain. Maybe they want to use his knowledge of the Cullen family or his unique vampire abilities (even if he doesn't remember them at first) for something sinister, like starting a war between vampires and humans.
A powerful and corrupt politician could be the main antagonist. He might be using his influence to cover up illegal activities, and Edward, as an honest cop, stands in his way. The politician could try to frame Edward or have him removed from the case.
Maybe a witch who has a vendetta against vampires in general. She could use her magic to cause all sorts of trouble for Edward, like casting spells that prevent him from using his vampire abilities or even creating illusions to drive him mad. Since she's a witch, she has different powers compared to a normal vampire hunter, so she'd be a very formidable antagonist. She might also be able to manipulate other humans or vampires to do her bidding in her quest to get rid of Edward.
One idea could be that Edward wakes up with amnesia and forgets his vampire nature. He starts living as a normal human, going to school and making new friends. This would lead to a lot of comical and also heart - wrenching moments as he slowly discovers his true self again.
It could be another alchemist who wants to use this new energy for evil purposes. This alchemist might see Edward as a threat to his plans and constantly try to stop him from learning more about the energy.
His parents or adoptive parents in the Cullen family are likely to be main characters as well. They would be responsible for taking care of baby Edward, so they play an important role in the fanfiction.
Often, antagonists are also important characters in jasper hale and edward cullen fanfiction. These could be rival vampire clans or individual vampires with malicious intents. They create conflict for Jasper and Edward, forcing them to use their powers and work together. The presence of these antagonists can drive the plot forward and also show different aspects of Jasper and Edward's personalities as they face these threats.
Perhaps a corrupt law enforcement officer. He might see Edward as a threat to his own illegal activities or simply want to bring down a powerful mob boss. And Edward's possessive nature towards his operations would make him a prime target for this antagonist. This officer could use underhanded tactics to try and break Edward's hold on the mob world.
Voldemort could be the main antagonist. He might see Alice's vampire abilities as a threat and want to use Harry to get to her. He could also be interested in using her powers for his own dark purposes.
Maybe a powerful and ancient being that has been awakened by the mixing of the two magical worlds of Harry Potter and Twilight. This being is enraged by the existence of both wizards and vampires and wants to wipe them out. Harry and Rosalie, being representatives of their respective groups, must join forces to stop this ancient and powerful foe. Their combined skills and the unique powers of their friends from both worlds would be crucial in this fight.
The plot could involve Edward taking over a failing company. He uses his supernatural abilities to turn it around. For example, his enhanced senses might help him detect lies from employees or competitors. His charisma, which is already a strong point, would be amplified as a CEO, attracting investors and top - tier talent.