You could have a house - elf use the 'Ps I love you' concept. Maybe Dobby writes these messages to Harry in his own special way, like using sock - shaped parchments. Or it could be a part of a magical potion's side effect. When a character drinks a certain potion, they start seeing 'Ps I love you' messages from someone they care about, but they don't know who sent them at first.
One unique way is to have a magical parchment that only reveals the 'Ps I love you' message when the recipient truly needs it. So, for example, if Harry is in a life - threatening situation, the parchment in his pocket suddenly shows the message from Ginny. Another way could be through a spell that projects the 'Ps I love you' message in the sky over Hogwarts for everyone to see.
There are fanfictions that take the 'Ps I love you' concept and put it in a time - travel scenario within the Harry Potter universe. For instance, an older character travels back in time and leaves 'Ps I love you' messages for their younger self or for someone they love. This adds an interesting twist to the story. Also, there could be a story where a character who is thought to be dead leaves behind these loving notes, which are discovered later and change the way other characters view their relationship.
Foxes could be part of a new magical species in the fanfiction. They could have their own language and culture within the wizarding world. For instance, they might live in a hidden part of the Forbidden Forest and have a special connection to nature magic that the main characters need to understand to defeat a new dark force. This would expand the world - building in the fanfiction.
The crow familiar could be a bridge between the Muggle and wizarding worlds in the fanfiction. It can interact with Muggle animals in a way that normal wizarding familiars can't. For example, it can communicate with crows in the Muggle park and learn things about the Muggle world that are useful to Harry. It could also have a connection to a magical constellation. When the stars align in a certain way, the crow gains extra powers, like the ability to fly faster or see through invisibility cloaks. And you could write a story where the crow's nest is a portal to a secret magical realm that only it and Harry can access.
One way is to have a Creepypasta - like curse befall Hogwarts. For instance, a curse that makes the staircases move in a truly chaotic and disorienting manner, similar to the unease that Creepypasta stories create. The students would have to navigate this new and scary situation, perhaps with some help from the teachers who are also baffled by this strange occurrence.
A pegasus could be a time - traveling familiar. It could take the main character back in time to witness important events in the Harry Potter universe's history. This would add an exciting twist to the story.
One unique way is to make the Tower of London a key part of a time - travel plot. Say, a powerful spell was cast in the Tower long ago that is now causing disruptions in the present - day wizarding world. Harry and his friends have to travel back in time to the Tower's past to stop the spell from being cast in the first place. The Tower could be filled with different eras of magic and different types of magical defenses that they have to overcome. Also, the Crown Jewels in the Tower could be magically enhanced items that have a special connection to the wizarding world, like they can be used to unlock a powerful magical vault.
One unique way is to make the dragon fire act as a form of communication. Imagine a dragon that can send messages through the patterns of its fire. In the fanfiction, the main character has to learn to decipher these messages to solve a mystery or prevent a disaster. Another idea is to have the dragon fire be a source of time - travel. When the fire engulfs a certain magical object, it can send the holder back in time, leading to all sorts of interesting plot twists in the Harry Potter universe.
You could make the heritage potion a key part of a mystery. Maybe it's the only thing that can solve a series of strange disappearances in the wizarding world. The characters have to track down the ingredients, which are scattered across different magical locations, and then brew the potion correctly. Along the way, they learn about different family heritages and how they might be connected to the mystery.
A unique way could be if a magical diaper is created that has special powers. Maybe it can fly like a broomstick or protect the wearer from dark magic. This would be a very different take on the normal use of a diaper in a story.
First, you need to check the official rules of the contest. Usually, there will be guidelines on things like word count, formatting, and the deadline. Then, you should re - read the 'ps i love you' story to get a good grasp of the characters and the plot. After that, start writing your own version of the story, making sure to be creative and stay true to the essence of the original in some way.