Well, perhaps Percy has been poisoned by a monster which is making him sick and his sneezes are a way of expelling the poison in a very strange way. His sneezes could start to change the environment around him, like turning the water in the camp's lake into a strange, fizzy substance. Grover could use his nature - sensing abilities to try and figure out what kind of poison it is, while Percy struggles with his increasing bouts of sneezing and the weakness that comes with his sickness.
One idea could be that Percy's sneeze accidentally triggers some sort of magical reaction. For example, it could cause a mini - tsunami in the middle of Camp Half - Blood because his powers are all jumbled up due to his sickness. Another plot could involve Percy sneezing and accidentally revealing his location to some monsters who are on the hunt for him while he's weakened by the illness. Maybe his friends have to figure out a way to keep him hidden and also cure his sickness at the same time.
His friends would first be really concerned. Annabeth would be in her problem - solving mode. She'd try to analyze the symptoms, not just the sneezing but also any other signs of Percy's sickness like his temperature or any strange marks on his body. Grover would stay by Percy's side, constantly offering moral support. He might also use his empathy link with nature to see if there are any plants that could help. Leo would likely try to invent some sort of device that could either stop the sneezing or figure out what's causing it, while Piper would use her charm - speak to try and soothe Percy when the sneezing fits get really bad.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One interesting plot could be Percy having to relive his adventures but with a different set of allies. Maybe some of the minor characters from the original series become major players this time.
One plot idea could be Percy seeking Hestia's guidance during a time of great turmoil in the demigod world. Hestia, being the goddess of the hearth, could offer him a sense of home and stability in a chaotic situation. Another idea is a story where Hestia tasks Percy with protecting an ancient relic related to the hearth that has the power to either save or destroy the camp. Or perhaps a fanfiction where Percy discovers a long - lost connection between his family and Hestia, which gives him new powers or a special mission.
One plot idea could be Percy and Hercules teaming up to defeat a new, powerful monster that neither could handle alone. Maybe it's a creature that combines the powers of Greek and Roman mythologies in a strange way. Another idea is a competition between Percy and Hercules in a modern - day Olympics - style event where they use their demigod powers.
One idea could be Triton and Percy teaming up to fight a new sea monster that threatens both the underwater kingdom and the surface world. This would bring out their different powers and personalities as they strategize together.
Another plot could be that Io is a reincarnation of an ancient demigod. Percy meets her and realizes she has memories of a time long past that could help solve some of the mysteries surrounding the origin of the demigods. They embark on a journey to find a lost temple where the answers lie. However, they face many obstacles like traps set by the Titans and the interference of some jealous gods.
Well, a cool plot might involve Percy's old enemies from the demigod world somehow influencing events at Goode. For example, a spell is cast that makes the students act like the minions of an ancient Greek villain. Percy then has to figure out how to break the spell without revealing his powers too much. Also, it could be interesting if there was a plot where Percy discovers a hidden part of Goode that has a connection to the gods, like a secret chamber that was built long ago by a demigod who attended the school.
A plot could involve Percy's friends being in danger and the only way to save them is by making a deal with the entities in the Styx. He might have to sacrifice something precious, like a part of his powers, in order to gain their help. This would create a great internal conflict for Percy as he weighs the cost of saving his friends against his own abilities.
One idea could be that Bianca doesn't die. Instead, she discovers a hidden power within herself that can control time briefly. This power comes in handy when she and Percy are in a dangerous situation against a powerful monster. They are trapped in a maze - like lair, and Bianca uses her time - controlling power to freeze the monster, allowing them to escape.