Who could be the main antagonist in a 'princess becomes a dragon fanfiction'?

Maybe an ancient dragon that has been awakened from its slumber and views Natsu as an intruder in the dragon world. Since Natsu is a new - made dragon, this old dragon might try to drive him out or even harm him.

It could be a dark wizard who wants to capture Hedwig - as - a - dragon for her powerful new form. Maybe he wants to use her dragon abilities for his own evil plans.

There could be a group of pure - blood wizards who believe that dragons are beneath them and that Harry is tainting the wizarding world by associating with them. They would try to stop Harry from his dragon - related activities, and they might use underhanded tactics like casting spells on him or trying to get him expelled from Hogwarts.

It could be a dark wizard who wants to control the dragons for his own evil purposes. He might see Harry as a threat because Harry is forming a bond with the dragons and teaching them to resist dark magic.

It could be a dragon hunter who sees Dean as a dangerous abomination. This hunter might have a personal vendetta against dragons and doesn't care that Dean was once human.

Perhaps an evil mage who has been researching on how to control dragons. When he hears about Natsu's transformation, he sees Natsu as a perfect specimen to experiment on. So he becomes the main antagonist, trying to capture Natsu and use his powers for his own dark purposes.

It could be an evil dragon slayer who is jealous of Natsu's new form. This antagonist might try to steal Natsu's power or find a way to turn him back to his normal self out of envy.

It could be Morgana. She might see Merlin's transformation into a dragon as a threat to her own power and plans. So, she tries to stop him from fully becoming a dragon or tries to use his new form for her own evil purposes.

Another option is a rival dragon slayer who sees Natsu's transformation as a threat to his own status. This rival could try to stop Natsu from fully becoming a dragon or try to defeat him to prove his own superiority.

Perhaps an ancient sorcerer who has the ability to control celestial dragons. He sees Lucy as an obstacle to his domination over the world using the power of these dragons. He would use his vast knowledge of magic and his control over the dragons to try and defeat her.