One possible plot twist could be that the pregnancy is part of a larger scheme by a third party. Maybe Voldemort or some other dark wizard has manipulated the situation to either gain control over Lucius or to use Harry's unborn child for some dark purpose.
I'm not aware of any such fanfiction that adheres to the original Harry Potter lore, as it goes against the established gender and biological norms of the series. Fanfiction often explores creative and sometimes out - of - the - box ideas, but this seems quite a deviation.
One possible plot twist could be that the girl who is pregnant has some sort of magical ability related to the pregnancy that no one expected. Maybe she can communicate with the unborn child in a magical way. Another could be that Harry discovers he's not the real father, but due to some magical mix - up, he has to take on the role anyway.
I'm not sure if there is such a fanfiction. Fanfiction can cover a wide range of very creative and sometimes out - of - the - ordinary ideas, but this one seems rather unusual. You could try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net to see if it exists.
One possible plot twist could be that it was all a misunderstanding or a magical prank. Maybe a mischievous character cast a spell that made it seem like Gon was pregnant by Hisoka, but in reality, it was just an illusion to create chaos. Another could be that the pregnancy is part of a prophecy that has far - reaching consequences for the entire world they exist in, and they have to figure out how to deal with it.
There may be such fanfictions in the vast world of fanfiction, but this kind of plot often goes against the original tone of the 'Harry Potter' series. It involves some rather unorthodox and out - of - character interpretations. Fanfiction can be very diverse, but this particular theme might not be widely accepted by all fans.
A really interesting plot twist could be that after getting pregnant, Lily loses her memory. So Snape has to deal with not only the fact that he's going to be a father but also that Lily doesn't remember their relationship. And then James steps in to help, thinking the baby is his. This would create a very strange love triangle situation. Also, what if the baby Harry has some sort of special power from the start that no one expected, which could be a major plot twist.
One possible plot twist could be that the pregnancy is the result of a magical accident or spell gone wrong. Maybe they were working on a new charm and something unexpected happened. Then they have to figure out how to deal with it while keeping it a secret from their enemies in the wizarding world.
One possible plot twist could be a magical mix - up. Maybe a spell gone wrong during a joint mission between Harry and Fleur. For example, a spell that was meant to protect them instead created a false pregnancy - like situation for Fleur. Another could be a prophecy that was misinterpreted, making everyone think Fleur was pregnant when in fact it was a sign of something else entirely related to the magic in the wizarding world.
It would be extremely strange and non - traditional. It would completely distort the normal relationships and biological rules in the Harry Potter world. Maybe it would involve some dark magic or some really out - there plot devices to make such a situation possible.
One possible plot could be that in a magical realm where the bond between Toothless and Hiccup is even more profound, an ancient spell or some kind of strange phenomenon causes Hiccup to be able to conceive. Toothless, being extremely protective, would then go to great lengths to keep Hiccup safe during the pregnancy. He might search for special herbs or a safe place for her to give birth. And along the way, they face challenges from those who don't understand this strange occurrence.