An octopus might be the toughest. Octopuses have eight arms that can move independently, which is a very complex form of locomotion to master. Percy would also have to deal with living in the water all the time and changing his color and texture to blend in with his surroundings. Plus, octopuses are very intelligent but in a different way from humans, so Percy would need to adapt to a new type of thinking.
A snake would be very challenging. Snakes move in a completely different way from humans or demigods. Percy would have to get used to slithering on his belly and seeing the world from a low, sideways perspective. Also, snakes have a different way of sensing their environment, like using their tongues to smell. Percy would need to adapt to this new way of experiencing the world.
A spider could be the most difficult. Not only does it have eight legs to control, but spiders also build webs and live in a very different social structure. Percy, as a spider, would have to learn how to spin silk and use it to create a home and catch prey. And the idea of being small and vulnerable compared to his normal self would be a big adjustment for him.
Perhaps Percy turns into a falcon. In this form, he could soar through the skies and spy on his enemies from above. He might use his falcon eyes to find a secret lair of a villain or to track the movements of the Titans. It would also give him a different perspective on the world around him, seeing things from a bird's - eye view.
Suppose Percy turns into a horse. His close friends might feel a sense of responsibility to protect him, especially if he's in a dangerous area. He could form a bond with other horses, and this might introduce new characters into the story. His relationship with his human family might become more complex as they struggle to understand his new state and how to interact with him as a horse.
One of the most challenging aspects is dealing with dangerous animals. For example, if it's a large, aggressive wild animal like a bear or a wild boar, it poses a great threat to the safety of the animal control officers.
One possibility is that Percy turns into a falcon. He could then use his new form to spy on his enemies from above. With his sharp eyesight, he might discover hidden lairs or secret meetings. This would give him an advantage in the story's battles or quests.
In a fanfiction, Percy's adaptation to Hogwarts would be a bumpy but interesting ride. He'd be constantly comparing Hogwarts to Camp Half - Blood in his head. At first, he might struggle with the lack of open combat training like he has at camp. But he'd discover that the dueling club at Hogwarts can be a substitute. He'd have to adapt to the different social hierarchies too. The pure - blood, half - blood, and Muggle - born concepts would be new to him. He'd probably see similarities to the god - parent, demigod, and mortal distinctions in his world. His loyalty to his friends from Camp Half - Blood would remain strong, but he'd gradually develop new loyalties at Hogwarts as well.
He'd have to learn the new rules. Percy is used to the Greek pantheon's way of doing things, but in Asgard, it's a whole different ballgame. He'd probably start by observing how the Norse gods and their followers interact. And he might use his charm, which has served him well in the Greek world, to make friends among the Norse.
Percy would likely first be shocked by the cold in Skyrim. But he'd quickly adapt his powers. He could use his control over water to deal with the snow and ice, maybe even creating steam to warm himself up. His fighting skills with a sword from his demigod training would be useful against the bandits and monsters in Skyrim.
Percy would need to learn how to be stealthy. He's used to fighting out in the open as a demigod, but as a ninja, he'd have to blend into the shadows. He could use his powers over water to create distractions or cover his movements, like making a mist to hide in.
He'd probably have a hard time at first. The weather in Forks is very different from what he's used to. Also, the small - town atmosphere might be a bit suffocating for someone who's used to the more adventurous life of a demigod. But he'd adapt by using his skills. His athleticism from all his training as a demigod would make him stand out in school sports, which could be a way for him to make friends.
Percy would probably have to adapt to the different cultural norms. For instance, the Soviet Union had a very different social and political structure compared to what Percy is used to. He might initially struggle with the more collective mindset. However, his ability to adapt quickly, which he has developed from his various adventures in the Percy Jackson series, would help him. He could start by learning the Soviet language, which would be essential for communication.