He might also have the power to sense chakra more acutely. This would help him in detecting enemies from a distance, finding hidden traps that are chakra - based, and also in understanding the flow of chakra within his own body better. He could use this power to train more effectively and also to teach others about chakra control.
He could have the power of super - speed. This would make him useful for quick getaways during missions or for quickly reaching strategic points. He could also use his speed to create distractions, like running in circles around enemies to make them dizzy.
He could have elemental magic like fire or ice. Fire magic would be really powerful, allowing him to create intense blazes to attack enemies. Ice magic could be used for both defense, creating ice barriers, and offense, freezing opponents. Another option could be summoning magic, where he summons mythical creatures to fight by his side. For example, he might summon a phoenix that can heal him with its flames or a griffin for its strength in battle.
One idea could be that the male OC is reborn into the Uzumaki clan during a time of great turmoil. He could use his knowledge from his past life to help the clan survive and thrive. Maybe he knows about upcoming threats and can prepare the Uzumaki for them.
The baby could potentially have Naruto's chakra powers. Since Naruto has a vast amount of chakra and can access the Nine - Tails' power, the baby might inherit some of that. Maybe it could also have some unique abilities from the OC. For example, if the OC has a special type of jutsu related to nature manipulation, the baby could have a combined form of that and Naruto's powers.
Well, he might gain special abilities by undergoing some sort of extreme physical or emotional trauma. In the story, Kaneki's transformation into a more powerful ghoul was partly due to the torture he endured. The male OC could experience something similar, which could trigger a latent power within him. Additionally, he could study ancient ghoul lore. There might be secrets hidden in the past of ghouls that could unlock new powers if he discovers and applies them.
The Sharingan gives the ability to see chakra, which in a Marvel context could be translated to seeing energy or life forces. So they could detect hidden enemies or sense the power levels of other characters. Also, the ninja skills would include things like super - fast movement, stealth, and proficiency with various weapons like kunai and shuriken.
He could have the power of light. Maybe he could create blinding flashes to disorient his enemies. Also, he might be able to control the sun's heat, using it in combat like shooting out beams of intense heat.
Maybe he has the power of elemental control. Given his Slytherin nature, water or air control would be fitting. He could use water to create barriers or air to send messages or eavesdrop on conversations. This would add a new dimension to his sneaky and resourceful character.
Percy could have his water - controlling powers from his original story. In the Avengers fanfiction, this could be really useful against fire - based villains or in situations where they need to manipulate water for various reasons, like putting out fires in a big city during an attack or using water to create barriers against enemies.
He might have the power of earth manipulation. Since Rhea is associated with the earth, Percy could gain the ability to control the ground, like creating earthquakes or forming barriers made of stone. This would be a very powerful addition to his existing powers.