The setting can make your fanfic stand out. Place the Beowolf xm in an unusual location within the RWBY universe. For instance, instead of the usual forest or city, have it be in an ancient underground ruin. The RWBY team has to navigate this new environment while dealing with the Beowolf xm. You can also introduce new elements in the environment that interact with the Beowolf xm, like some sort of magical crystals that affect its powers.
A good way to make it stand out is through the plot twists. Have the Beowolf xm not be what it seems at first. It could start off as an enemy but then turn out to be a key to solving a much larger problem in the RWBY world. For example, it might hold the secret to a new form of Dust that can be used to fight all Grimm more effectively. And as the RWBY team uncovers this secret, they have to protect the Beowolf xm from other parties who want to use it for their own evil purposes.
One idea could be a Beowolf that has some unique mutation (xm could imply a special mutation perhaps) and it forms an unexpected alliance with a RWBY character. For example, it could be that the Beowolf has a special ability to sense danger in a different way and it warns Ruby of an upcoming large Grimm attack. This could lead to Ruby trying to understand if the Beowolf can be tamed or not.
Focus on unique character interactions. For example, if you have a Forerunner character interacting with Ruby, show how their different worldviews clash or complement each other. Ruby's optimism and the Forerunner's more advanced technological mindset could lead to interesting conversations.
Add unexpected plot twists. Maybe the villain that the heroes thought was the main threat is actually just a pawn. The real villain is someone they least expected, like a seemingly innocent bystander or a member of their own team who has been secretly working against them all along. This will keep readers on their toes and make your fanfic more engaging.
Develop a complex backstory for the Demon Grimm. Explain how it came to be, what its motives are, and how it relates to the overall lore of RWBY. For example, it could be the result of a long - forgotten experiment by an ancient civilization that once existed in Remnant. This would add depth to your fanfic. You can also include some unexpected plot twists. For instance, the Demon Grimm could have a secret weakness that is only revealed through a series of events and investigations by the RWBY characters. This keeps the readers on their toes and makes your fanfic more engaging.
Give your OC a distinct personality trait. For example, if all the RWBY characters are brave and confident, your OC could be shy but extremely intelligent. Another way is to give them a unique fighting style. Maybe they use an ancient form of combat that no one in the RWBY world has seen before. Also, their backstory can set them apart. If they come from a long - lost tribe of Faunus with special powers, that would make them very interesting.
Well, if you want your RWBY humanoid Grimm fanfic to be outstanding, you should consider the world - building aspect. Expand on the RWBY world by introducing new locations related to the humanoid Grimm. Maybe there's a hidden lair where they breed or a special dimension that they come from. Character development is also crucial. Let your humanoid Grimm grow and change throughout the story. It could start as a mindless killing machine but then develop emotions or a sense of purpose. Additionally, incorporate some mystery elements. Leave some questions unanswered at the beginning, like the origin of the humanoid Grimm, and gradually reveal the answers as the story progresses. This will keep the readers hooked.
Give your OC a distinct appearance. For example, if they are a gamer, they could have unique gaming - related accessories like a customized headset or a controller - shaped weapon. Also, a special semblance that is different from the common ones in RWBY, like the ability to teleport through virtual portals.
To make it stand out, create a really unique OC. Maybe give them an unusual semblance or a strange backstory. Also, focus on character development. Show how your OC grows and changes throughout the story.
Develop an original plot. Instead of the typical 'stop the bad guy' plot, have the crossover be about something different. Say, a competition between the two universes where Megaman and the other crossover character have to prove which world has the better heroes. This will draw readers in as it's not the usual storyline.
It can stand out through its creativity in power - ups. If the fanfic gives characters really unique and extreme power - ups, it'll draw readers. For example, giving Blake the ability to teleport through shadows at will, which is a huge departure from her normal abilities in the show.