Maybe he could gain the ability to transform into an Egyptian animal, like a falcon or a jackal. This would be a cool addition to his existing powers and would give him new ways to move around and fight enemies.
Another possibility is that he could gain some form of sand - based power. Given the importance of the desert in Egyptian mythology, Percy could control sand, perhaps using it to blind enemies or create barriers, similar to how he uses water in the original Percy Jackson stories.
He could gain the power of super strength that far surpasses his demigod strength. This would allow him to lift extremely heavy objects or even mountains. Another power might be the ability to control the very essence of the ocean on a global scale, not just local waters like he could as a demigod.
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.
He could gain the power of controlling water like Poseidon's kids since he has good chakra control. It would be a new addition to his skill set.
Perhaps he gets the power of astral projection. He could send his spirit out of his body to explore areas that are otherwise inaccessible or to spy on his enemies. This would be a very useful power especially when dealing with secretive foes or trying to find hidden places in the mythological world.
One possible new power for Percy Jackson in fanfiction might be the ability to communicate with all types of mythical creatures, not just those related to the sea. This would expand his network of allies and give him more knowledge about the mythical world.
Well, in fanfiction, Percy could have the power to control storms on a global scale. Imagine him summoning massive hurricanes to defeat his enemies or using gentle rain to heal the land. It would be a huge upgrade from his existing water - based powers.
In Percy Jackson new elemental powers fanfiction, the power of time could be a new addition. A character might be able to slow down or speed up time in a small area, affecting the elements within it. For instance, if they slow down time around a fire, it would seem to burn more slowly. Also, the power of space could be introduced. This could allow a character to manipulate the space between elements, like pulling water from a far - off source or compressing air to create a powerful blast.
He could go on adventures to the far reaches of the Underworld. With all the gods' powers, he might be able to access areas that were previously off - limits. He could also journey to the homes of the gods and goddesses to learn more about their powers and how to use them better.
One way could be through magic systems. Maybe Percy's water - controlling powers could interact with Egyptian magic in some unique way. For example, the Egyptian magic related to the Nile River could be linked to Percy's abilities.
He could gain better detective skills. Batman is a master detective, and Percy could learn to analyze situations more carefully, like looking for hidden clues in a mystery involving the gods or monsters. For example, when trying to find out who stole a powerful artifact, Percy could use Batman - like deductive reasoning.