First, decide on their backstory. Maybe they had a rough childhood in one of the hidden villages that led them to turn bad. For example, if they were from the Hidden Leaf, they could have been shunned for not having strong ninja skills initially. Then, design their appearance. They might have a unique hair color or style, like long white hair to give an air of mystery. Also, think about their abilities. It could be a special jutsu related to shadows or something that's not commonly seen in the Naruto world.
A villain oc who is a half - human, half - beast hybrid. They were outcast from society because of their appearance and now seek revenge on all the villages. They have unique physical abilities due to their hybrid nature, like super strength and enhanced senses. Or perhaps a villain oc who is a former student of a great ninja but turned against their teachings. They create their own new and dangerous form of ninjutsu that goes against the traditional ways.
Title: 'The Rise of the Shadow Serpent'. In this fanfic, my villain OC is the Shadow Serpent. She was once a kind-hearted girl, but after being betrayed by those she trusted, she turned to the dark side. She uses her power to create illusions and chaos in Paris. Ladybug and Chat Noir face a tough battle as they try to figure out her motives and weaknesses.
A new villain could have the power of time manipulation, but only in small bursts. For example, they could slow down time for a few seconds to dodge Batman's attacks or speed it up to escape. They might also have the power to absorb and redirect energy. So if Batman uses his batarang with some sort of energy enhancement, the villain could absorb that energy and send it back at him. Another cool power would be the ability to teleport through mirrors, using Gotham's many reflective surfaces to their advantage.
For a Miraculous Ladybug villain OC fanfic, consider an OC called the Sound Shredder. This villain can emit ultrasonic waves that can shatter glass and disrupt Ladybug and Chat Noir's communication. He was a former musician who lost his hearing due to an accident and now wants to make the world feel his pain. Also, the Frost Fang OC could be a great addition. She has the power to freeze everything in her path. Her backstory could be that she was left out in the cold, literally, by her friends and now seeks revenge on the whole city.
The main villain could be a big - city developer who wants to destroy the Chipmunks' forest home where the OC also lives. He is greedy for land and doesn't care about the animals or the environment. The OC and the Chipmunks have to come up with a plan to stop him, like getting the local community to protest against his plans.
I really like 'Villainous Intent: An OC's Tale'. This fanfic does a great job of integrating the OC villain into the existing BNHA world. It shows how the OC interacts with the well - known heroes and villains from the original story, and the plot twists are really exciting.
Often, bnha female villain oc in fanfic are highly intelligent. They need to be smart to outwit the heroes. They can plan elaborate schemes and manipulate situations to their advantage. Also, they tend to have a certain charm or allure. This helps them in getting what they want, whether it's influencing other characters or distracting their enemies. In addition, many of them are quite independent, not relying on others to achieve their goals.
Isolation is also a theme. Naruto has always craved acceptance. If he is pushed into a corner and isolated completely, he may turn to villainy. He might think that if the world won't accept him as he is, he'll make the world fear him. This theme can explore the psychological effects of loneliness and rejection on a character as powerful as Naruto.
It could be an evil version of Victor himself. Maybe in an alternate timeline or due to some dark magic, Victor turns bad. His knowledge of the Justice League and his own powers would make him a formidable foe. He could be trying to take over the world or exact revenge on the League for something that happened to him in the past.