Play with the rules of the powers. In the fanfic, you could introduce a situation where Danny's Ghostly Wail is not as effective as he thought. Maybe there's a new type of ghost or entity that is immune to it. This forces Danny to find new ways to use his other powers and team up with his crossover partners in different ways to overcome challenges, making the fanfic stand out.
Focus on character development. For instance, if you're crossing over with a character from another series, show how Danny's Ghostly Wail affects that character's view of the supernatural. Maybe they were skeptical before, but after seeing the power of the Ghostly Wail, they start to believe. This can create an interesting dynamic between the characters.
Incorporate unique settings. Instead of the usual Amity Park, set the crossover in a completely different location, like an underwater ghost city. Danny's Ghostly Wail could have different effects in this new environment, like causing underwater tremors. This can add a fresh twist to the story.
Another idea is a crossover with a superhero universe. Imagine Danny Phantom's Ghostly Wail being used in a fight against some supervillains. He could cross paths with a young superhero who is initially scared of Danny because of his ghostly appearance. But when they see how Danny uses his powers, especially the Ghostly Wail, for good, they team up. Danny could teach the superhero about the ghostly realm and how to deal with supernatural threats.
One interesting Danny Phantom Ghostly Wail fanfiction could be about Danny exploring the full extent of his Ghostly Wail power in a new dimension. Maybe he discovers that in this dimension, the wail can not only repel ghosts but also heal certain spectral entities.
Jazz, Danny's sister, is also a common character. She might be the one who tries to understand Danny on a more emotional level when the power of the Ghostly Wail starts to take a toll on his mental state. For example, she could be the one to talk him down when he's frustrated about not being able to control it properly.
Yes, there are some interesting ones out there. You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'danny phantom ghostly harem' and you'll find a variety of stories with different takes on the concept.
Check out blogs dedicated to Danny Phantom. Some bloggers review or recommend fanfics. They usually give a brief summary of what the fanfic is about and what makes it good, which can help you decide if it's the best Danny Phantom crossover fanfic for you.
One way to make it unique is by adding unexpected twists to the plot. For instance, instead of Danny always being the hero, what if there was a time when he was wrongly accused of causing chaos in the human world and had to prove his innocence while also fighting real threats? Also, you could play with the concept of time. Maybe Danny gets sent back in time to when his powers first emerged and has to relive that part of his life with his current knowledge, which could lead to some really interesting changes in the storyline.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, and there are likely to be some Danny Phantom Ghostly Lemon ones there.
One common theme is the supernatural aspect. Since it involves Danny Phantom and ghosts, there's often a lot of exploration of the otherworldly powers and how they interact with the harem dynamic. Another theme could be love triangles or more complex relationship webs within the harem.
Another unique part is the way these fanfics can blend horror and action elements. Danny's possession can be a really spooky concept, like in some stories where he loses control of his body. But at the same time, there are always action - packed scenes as he tries to regain control or fight against the possessing force. It creates a great balance that sets these fanfics apart from other types of fan works.
The combination of different power systems. Danny has his ghost powers like intangibility and flight, while RWBY characters have their Semblances and use of Dust. When these are combined in a fanfic, it creates a really unique dynamic.