One possible antagonist could be a dark wizard who hears about Harry's attempt to create the Philosophers Stone. This wizard, who was once a follower of Voldemort, wants to steal the Stone for his own gain. He might try to infiltrate Hogwarts and cause chaos. Another antagonist could be a jealous student at Hogwarts. This student is envious of Harry's skills and popularity and wants to stop him from creating the Stone out of spite.
One idea could be that Harry discovers a hidden spellbook in the Room of Requirement that has ancient alchemical knowledge. He uses this to recreate the Philosophers Stone, but with a twist. Maybe he wants to use it to heal all the students who were injured during the Battle of Hogwarts. Another idea is that Harry creates the Stone in secret and uses it to gain more power to fight against the remaining Death Eaters. However, he soon realizes that power from the Stone comes with a great price and he has to make a difficult choice.
One possible main antagonist could be a powerful Grimm lord that has emerged. This Grimm lord could be far more intelligent and organized than regular Grimm, and it sees Ruby's growing army as a threat to its plans of total domination. It could send out waves of Grimm to attack Ruby's army during its formation, trying to disrupt and destroy it.
Some pure - blood supremacist families who don't approve of their marriage could be antagonists. They might try to cause trouble for Harry and Luna, maybe by spreading false rumors or trying to undermine their work in the wizarding world.
The Ministry of Magic could be the antagonists. Since Harry is in a gang, they might see him as a threat to the order of the wizarding world. They could send Aurors after him and his gang mates, trying to arrest them and break up the gang.
Harry is the main one, but other characters could be involved in different ways. Neville could accidentally stumble upon Harry's secret project and, in his clumsy but kind - hearted way, end up helping. Luna Lovegood might offer some out - of - the - box ideas with her unique perspective on magic. And Dumbledore, with his vast knowledge and wisdom, could be a guiding figure in the background, giving Harry some cryptic advice that helps him in the creation of the Firebolt.
Dumbledore, even if in spirit or through some magical means, could be an ally. His wisdom and foresight could guide Harry in making important decisions for the kingdom. Also, the house - elves, if Harry treats them fairly and gives them freedom and a place in the kingdom, could be loyal allies. They could take care of the day - to - day running of the castle or important buildings in the kingdom, using their unique magical abilities.
The Ministry of Magic could turn into an antagonist. If Harry's new cold and strong ways are seen as a threat or too radical, they might try to stop him. This could lead to a conflict between Harry and the wizarding government.
A new dark wizard could emerge in the wizarding world. This wizard might be jealous of Harry's fame and power and think that by getting to Lily, he can gain some sort of advantage. He could try to steal Lily's magic or use her to spread fear in the wizarding community.
The Thalmor could be great antagonists. Their strict control over magic and their anti - human beliefs could put them at odds with Harry. They might see his different form of magic as a threat to their power in Skyrim.
Some of the more traditional pure - blood families in the wizarding world could be antagonists. They might not approve of Harry, a half - blood, being involved with Pansy, and they could try to stop the pregnancy or break up the couple for the sake of 'pure - blood' ideals.