Well, Percy could potentially have the power of hydro - kinesis, which means he can control water in all its forms - liquid, solid (ice), and gas (steam). In the context of an Avengers fanfiction, this power could be used in countless ways. For example, he could create ice bridges to cross difficult terrains, use steam to blind enemies, or create huge water columns to lift the Avengers up to a higher vantage point. He might also have some sort of connection to sea creatures, and be able to call them for help in battles, which would add a really unique aspect to the Avengers' team.
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.
Percy can communicate with sea creatures. This may seem a bit odd for the Avengers at first, but it could actually be very useful. Sea creatures could act as scouts in areas near water, providing the Avengers with early warnings of approaching threats. Also, some sea creatures have healing properties themselves, and Percy could potentially use his connection with them to find new ways to heal the Avengers.
Maybe Naruto would have the power of cosmic energy projection. He could shoot out powerful blasts of energy that are a mix of his chakra and cosmic forces. This would be a great offensive weapon against the Avengers' enemies.
Another possibility is that the baby has a combined power. It could use water to create illusions, a mix of Percy's water control and Annabeth's strategic thinking. So when in a fight, it could create false images of itself using water to confuse the enemy and then attack from an unexpected angle.
As a demigod, he might have superhuman strength, speed, and the ability to control water. As a magician, he could have the power to cast spells. For example, he could combine his water - controlling ability with a spell to create ice sculptures with magical properties. He might also be able to teleport short distances using magic, which is different from any demigod power he has.
In this fanfiction, Percy could have an ability to sense danger. It's like a sixth sense that warns him of impending threats. This could be a natural ability that he has had since birth. He could also have a talent for hacking, which he learned from Tony or on his own. With this, he can access secure systems to gather information or disable enemy technology. And perhaps he has a unique way of thinking that allows him to come up with out - of - the - box solutions to problems that Tony and his team face.
Well, if Percy is the son of Loki in a fanfiction, he could inherit Loki's ability to manipulate minds to some extent. This would give him an advantage in getting out of tricky situations. He might also get Loki's power of teleportation or at least some form of fast movement. And considering Loki's connection to chaos, Percy could have an innate ability to disrupt magic or technology around him. His water - based powers from his Greek side could be enhanced with Loki's chaotic energy, making his control over water more unpredictable and powerful.
It might have the ability to absorb and redirect magic. If an enemy casts a spell at Percy, the katana could absorb the magic and then send it back at the attacker, amplified. This would give Percy an edge in battles against magic - using enemies, as he could turn their own magic against them with the help of the katana.
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.
They could have a mini - adventure within the quarantine zone. Maybe they discover a hidden room in the compound that has some sort of mystery element. For example, it could be a room filled with old technology from the early days of S.H.I.E.L.D. that they have to figure out how to work. Or they could have a cooking adventure, with Thor trying to make Asgardian food and everyone else either being horrified or pleasantly surprised by the results.
Percy's powers would be a great addition to the Avengers in a fanfiction. His control over water could create a lot of strategic opportunities. He could flood an area to slow down enemies or create ice platforms for the Avengers to stand on during battles. Compared to Captain America's leadership and combat skills, Percy could offer a different kind of support. And when it comes to Thor, while Thor controls lightning, Percy could use water to conduct that lightning in different ways for more powerful attacks.