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.
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.
In a more complex way, Percy's interactions could be influenced by the political situation between the Greek and Egyptian gods. If there's some sort of tension between the two pantheons, the demigods might be caught in the middle. Percy would have to be diplomatic and try to find ways to keep the peace while still maintaining his own beliefs and loyalties. For example, if there was a dispute over a powerful magical artifact, Percy and the Egyptian demigods would have to figure out how to resolve it without starting a full - blown war between their respective godly parents.
I really like 'Percy and the Magic Arts'. In this fanfiction, Percy discovers he has a hidden talent for magic in addition to his demigod powers. The author does a wonderful job of exploring how he would balance these two aspects of himself. It's full of action, with Percy facing off against magical creatures that are new even to him.
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.
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.
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.