Maybe a plot twist could be that Sam's transformation into a kid is part of a larger, more sinister plan by an unknown entity. This entity could be using Sam as a child to manipulate Dean in some way, perhaps by making Dean over - protective and leading him into a trap.
A really cool plot twist could be that Sam's kid form has some new and unexpected powers. Since he's in a different physical state, his connection to the supernatural could be altered. He might be able to communicate with spirits in a way he couldn't as an adult, and this new ability could be the key to solving a major mystery in the fanfiction.
Dean would probably be very protective. He's always been the big brother looking out for Sam, and with Sam as a kid, that instinct would be even stronger. He'd be constantly worried about Sam getting hurt and would keep him close at all times.
One common plot twist could be that the curse is related to a powerful supernatural entity that wants to use Sam's unborn child for some dark purpose. Maybe it's a demon who plans to possess the baby as soon as it's born. Another could be that the pregnancy is a false one, created by the curse to deceive Sam and his friends into believing he's carrying a child, when in fact it's a trap to lure them into a dangerous situation. For example, it could be a spell by a witch to get revenge on Sam for something he did in the past.
One interesting plot twist could be that when Natsu turns into a dragon, he loses his memory of his human friends. This would create a lot of drama as his friends try to bring back the Natsu they know. Another could be that he turns into a different kind of dragon than expected, perhaps one with a very rare and powerful ability that attracts the wrong kind of attention from dark forces in the fanfiction world. And also, he might transform into a dragon at a crucial moment during a battle, not only surprising his enemies but also his allies, changing the whole dynamic of the fight.
One interesting plot twist could be that Hermione, as a vampire, still retains her thirst for knowledge. Instead of blood, she discovers a way to feed on knowledge energy. For example, she might visit ancient libraries at night and absorb the knowledge stored in the books, which gives her a different kind of 'nourishment'. Another plot twist could be her relationship with her friends. Harry and Ron might initially be scared of her, but then they realize that she's still the same Hermione deep down. They could then team up to fight against vampire hunters who see Hermione as a threat just because of what she's become.
Another interesting twist could be that the kidnapping was part of a test set up by Death himself to see if his son can handle difficult situations. This would completely change the perspective of the whole situation and add a new layer of complexity to the fanfiction.
One interesting plot twist could be that Bella's transformation into a vampire gives her a unique power that no other vampire has. For example, she might be able to control the weather. Another twist could be that instead of joining the Cullen family right away, she runs off on her own to explore the vampire world. Maybe she discovers a whole new coven that has different values and ways of life compared to the Cullens.
A great plot twist could be that Percy's transformation into a woman is not just a physical one but also gives her new powers or a different connection to the gods. Maybe she can now communicate with a goddess in a way that male Percy couldn't, and this new connection helps her on her quests in ways that are unexpected and exciting.
One interesting plot twist could be that Lincoln discovers he has a natural talent for something that is more associated with girls, like ballet. He might initially be embarrassed but then decides to pursue it wholeheartedly. Another twist could be that his transformation into a girl is only temporary, and he has to race against time to reverse it before a big event in his life, like a school play where he's supposed to play a male role.
One common plot twist could be Zuko, as a girl, having to navigate the same political challenges but with new gender - based obstacles. For example, she might face different expectations in the Fire Nation's patriarchal society. Another could be a romantic sub - plot where characters who previously interacted with male Zuko now have different dynamics with her as a female. Also, Zuko might use her new form to her advantage in disguise, perhaps infiltrating an all - female group to gain information for her cause.
One common plot is exploring what could have happened if Madison had survived. Maybe she and Sam could have had a life together away from the hunting world, like living in a small town and trying to be normal.