Well, in some modern Little Mermaid fanfictions, a plot twist is that the mermaid has a special power. For example, she can control water not just in the ocean but also in the human world. So when she becomes human, she has to hide this power. Also, instead of the traditional love story, the prince might be in love with someone else at first, but the mermaid's kindness and unique abilities make him fall for her in the end. Another interesting twist is that the mermaid's family comes to the human world to take her back, but she has to choose between her new life and her old family.
One unique plot twist could be that the mermaid is a famous singer in the human world. Instead of trading her voice for legs, she uses her singing talent to blend in. Another could be that the prince she falls for is actually a mermaid in disguise who has come to the surface to find a way to save their underwater kingdom. And sometimes, in modern fanfiction, the mermaid might be a scientist who discovers a way to transform herself into a human to study our world.
Maybe in the fanfiction, it turns out that the mermaids in 'The Little Mermaid' are actually part of an ancient prophecy related to 'Gravitation'. For example, they are the key to saving the world in 'Gravitation' from some sort of musical apocalypse. This would turn the whole story on its head as the characters from 'Gravitation' would have to rely on the mermaids and their unique abilities, which are completely different from what they are used to in their own world.
A really unexpected plot twist could be that Ariel's baby is not fully human or mermaid, but some sort of hybrid with unique powers. This would make her pregnancy a target for those who want to use the baby's powers for their own gain. Ariel and Eric would then have to fight to protect their family and their baby from these threats, and it could lead to a whole new adventure in the world of 'The Little Mermaid' fanfiction.
One interesting twist could be that Ariel's sisters find a way to break Ursula's spell on Ariel without the need for true love's kiss. They combine their own magic powers, which they have been secretly developing, and free Ariel from the deal she made with Ursula. This would completely change the course of the story as Ariel would no longer be in a race against time to win Eric's love.
A great plot twist in modern day Hunger Games fanfiction could be that the tributes discover that the whole Hunger Games is a virtual reality simulation and they are not actually in danger of dying. This would completely change the dynamic of the story.
One common plot twist is that Bella's mermaid identity is revealed in a very unexpected way. Maybe during a swim with the Cullens, she suddenly transforms, shocking everyone. Another is that her mermaid powers are somehow connected to the Volturi's plans, adding a new layer of danger.
In a modern little mermaid story, perhaps the mermaid is a marine biologist in human form by day. She uses her knowledge of the ocean to fight against pollution and over - fishing. One day, she meets a human man who is also an environmentalist. They fall in love while working on a project to save a coral reef. But she has to keep her mermaid identity a secret until she realizes that he will accept her as she is.
One idea could be exploring Ariel's life after she becomes human. Maybe she has trouble adjusting to some of the more mundane aspects of human life, like cooking or doing laundry. Another could be a story where Ursula's sister comes to seek revenge, but Ariel has to convince her that not all humans are bad.
One idea could be exploring the relationship between Melody and a new mermaid friend from a different part of the ocean. They could go on adventures together and discover hidden treasures.
Another plot could be about the mermaid learning more about the human world in a different way. Instead of just falling in love with the prince, she discovers a hidden talent among humans like music or art and tries to bring it back to the underwater world. This could create a whole new set of adventures and challenges for her. For example, she might have to find a way to communicate with a human artist without revealing her true identity at first.
One idea could be exploring what would happen if Ariel had a secret power she didn't know about until after she became human. For example, she could have the ability to communicate with all sea creatures, not just the ones she already knew. This would create new challenges and relationships on land.