Give the character a distinct appearance. For example, the OC Guru could have a long, flowing robe with strange symbols on it. And his eyes could glow when he uses his special powers.
Think about the character's backstory. If the OC Guru was once a great thief himself but gave it up for some noble reason, like he accidentally hurt an innocent person during a heist. This past experience shapes who he is now and how he interacts with the Cooper gang.
Perhaps the OC Guru is an old friend of Sly's father. So, he has a lot of stories and knowledge about Sly's family history. This could add a new layer of depth to Sly's character development as he learns more about his past through the Guru.
The OC could also be a long - lost relative of Sly. Maybe they were separated when they were young. As they meet again, they have to figure out how to work together while also dealing with their shared past and the secrets it holds.
Think about their backstory. For example, if they grew up in a different part of the world from Sly, what kind of environment influenced them? If they grew up in a city full of traps and puzzles, they might be really good at solving those types of challenges.
An OC that is a reformed enemy could be really cool. For example, a character who used to work for one of Sly's nemeses but saw the error of their ways. Their knowledge of the enemy's lairs and plans could be a great asset to Sly's team. They would also have to earn the trust of the gang, which could create some interesting storylines.
Create a strong plot that involves both Sly and the OC. It could be a mission they go on together, or a mystery they have to solve. Also, don't forget the relationships. Show how the OC interacts with Sly and his friends. Are they friends? Rivals? Lovers? The dynamics between the characters are important for a good fanfic.
Give your OC a unique backstory. For example, if they grew up in a different country but moved to Ikebukuro, it can shape their perspective. Also, a distinct physical trait like a scar or a unique hair color can make them stand out.
Give them a unique power. For example, if they can control the weather, it would be different from the existing powers in the Incredibles world. Also, give them a distinct personality. Maybe they are really shy but when they use their powers, they become confident.
To create a memorable character for a 'ben 10 oc fanfic', start with their powers. Make them something that stands out, like the ability to communicate with inanimate objects. Then, develop their personality around that power. Are they shy because they think their power is strange? Or are they confident and use it to their advantage? Their relationships with other characters in the Ben 10 universe also matter. If they have a rivalry with one of Ben's aliens, it adds depth to the character.
One idea could be to create an OC who is a long - lost relative of Sly. Maybe a cousin who has been living in a different part of the world and has unique thieving skills. They could show up and initially be seen as a rival to Sly but later turn out to be an ally. Another idea is an OC that is a magical creature that befriends Sly and his gang. This creature could have powers that help them in their heists, like the ability to become invisible or teleport short distances.
One great 'Sly Cooper fanfic' could be the one where Sly teams up with an unexpected character from another game universe. It adds a whole new level of adventure. Another interesting one might be a fanfic that delves deep into Sly's family history, exploring secrets that were never fully revealed in the original games. There are also fanfics that focus on the relationships between Sly and his friends, like how Bentley and Murray support him in different ways during their heists.