Another option for the main antagonist could be a spirit of an ancient Greek scholar who was banished from the world of the gods. This spirit haunts the Greek class and tries to possess Percy because he sees Percy as a way to get revenge on the gods. It causes chaos in the class, making it difficult for Percy to focus on his studies and also putting his friends at risk.
Perhaps Percy could have a dream during Greek class about an upcoming prophecy related to the class. In the dream, he sees that a certain ancient Greek artifact hidden in the school is going to be discovered, and it will either bring great danger or great power. So, he spends the rest of the class trying to figure out how to stop or find it first. Also, he could get into an argument with a teacher who doesn't believe in the real existence of the Greek gods, but Percy has to prove it without revealing his true identity as a demigod.
His water - controlling powers could cause some interesting situations. For example, if there was a leaky faucet in the classroom, he could accidentally make the water spray everywhere in a fit of distraction. Or he could use it to create a cool mist during a hot day to cool down the classroom, much to the surprise of his classmates.
Well, he might get some strange looks from his classmates. Some might think he's just showing off or being weird. But if there are any other demigods in the class, they could be secretly impressed or even a bit envious that he's so casually using Greek.
Perhaps Percy would use his knowledge of Greek gods and goddesses to impress the teacher. He could share some unique insights about a particular deity that are not commonly known. This could lead to him getting special privileges in the class, like being excused from a difficult assignment or getting extra credit.
One idea could be to write a fanfiction where Percy visits an ancient Greek city that has been forgotten by the modern world. He discovers a hidden power there that could change the fate of the demigods.
One way could be to describe the shock on his classmates' faces. For example, 'Percy blurted out a Greek phrase in the middle of class, and everyone's jaws dropped.'
Another great read is 'Percy and the Lost Greek City'. It's about Percy stumbling upon a lost Greek city that has been frozen in time. He has to figure out how to free the city and its inhabitants, all while facing off against some old and powerful foes.
One great 'Percy Jackson Roman and Greek Fanfiction' is 'The Lost Hero's Return'. It continues the story in an exciting way, with the characters facing new challenges. The author does a great job of staying true to the original feel of the series.
One possibility is that the Greek class is a place for Percy and Annabeth to show their relationship development. They could be paired up for a project on a particular Greek hero. While working together, they start to understand each other better. Annabeth might be really into the research part, while Percy brings in his practical understanding of how the hero's traits could be applied in a real - life - or rather, demigod - life - situation. And through this, their bond deepens as they both contribute their unique perspectives.