In this 'dean becomes a dragon supernatural fanfiction', it could start with Dean being in a fight with a powerful demon. During the battle, the demon casts a spell that backfires and instead of killing Dean, it turns him into a dragon. Dean then has to deal with the fact that he is no longer fully human. He may have to hide from other hunters who might see him as a threat. Meanwhile, he tries to figure out how to use his new dragon abilities to continue his fight against the supernatural, all while trying to find a way to turn back to his normal self.
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.
Maybe Dean gets cursed by a witch. The tail could be a side - effect of the curse that slowly changes him. He has to find a way to break the curse while still hunting monsters, and Sam has to deal with his brother's new 'accessory' and the problems it causes during their hunts.
Well, it could be that Hiccup is cursed by an evil sorcerer who wants to turn him into a dragon as a form of punishment. But as he turns into a dragon, he finds that he has a new connection with the dragon world. He starts to see things from a dragon's perspective and uses this to bring peace between humans and dragons in a whole new way.
Maybe Natsu discovers a new magic spell that accidentally turns him into a dragon. He then has to figure out how to reverse it while dealing with the new powers and instincts.
Well, perhaps Hedwig could be magically transformed into a dragon. Then she might go on adventures, using her new dragon abilities like flying faster and breathing fire to protect her wizard friend from dark forces.
She could be a nephilim, half - angel and half - human. This would put her in great danger as both angels and demons would be after her. Sam and Dean would have to constantly protect her and figure out a way to keep her powers in check.
Well, it could involve Issei discovering some ancient dragon magic. Maybe he stumbles upon a dragon's lair and is blessed with dragon powers. He might start to have dragon - like instincts, like a strong urge to hoard treasures or protect a certain territory.
Well, one plot could be that the princess is cursed by an evil sorcerer to turn into a dragon. As a dragon, she discovers new powers and a different perspective on her kingdom. She might initially struggle to control her new form but then learns to use it to protect her people from threats that normal human means couldn't handle.
Well, perhaps the plot could involve Natsu's transformation being a result of some powerful magic or a dark curse. He might struggle to control his new dragon form at first, causing chaos among his friends and allies.
One possible plot could be that Natsu is cursed by a dark wizard. This curse slowly transforms him into a fire dragon. As he changes, he struggles to control his new dragon - like instincts and powers. His friends initially fear him but then realize they need to help him break the curse.