Well, he might encounter rare and dangerous beasts. Maybe he discovers a hidden power source or an ancient artifact. He could also meet some reclusive and powerful shinobi who have made the forest their home.
Naruto in the Forest of Death in fanfiction might form alliances with the native creatures. He could befriend a giant snake or a group of intelligent monkeys. These new allies could help him in his future battles or in uncovering the secrets of the forest. Also, he may find a secret training ground within the forest that was once used by a great ninja in the past, and use it to enhance his skills.
He might have battles with strange creatures. In fanfiction, the Forest of Death is full of unknown threats. Naruto could discover new jutsus while trying to survive there.
In the fanfiction, Naruto could have adventures like finding a secret waterfall in the forest that has special chakra - enhancing properties. He might have to fight off bandits who are trying to take over the forest for their own evil purposes. And he could also meet a hermit who teaches him some new jutsu that are specific to the forest environment.
He might have adventures like befriending forest animals. Maybe he discovers a hidden magical spring in the forest that has special powers.
He could encounter rogue ninjas. They are always lurking in dangerous places like the Forest of Death, looking for easy prey or valuable items.
He could have adventures with the local wildlife. Maybe he has a close encounter with a moose or a bear. Or he could be exploring the vast, icy landscapes and discover some hidden caves filled with ancient artifacts.
They could face a new and powerful enemy that wasn't in the original story. Maybe a strange beast that has the ability to manipulate shadows in the dark forest. Naruto would be all fired up to fight, while Sakura would be using her intelligence to figure out its weaknesses.
She could have encounters with magical creatures that are rarely seen outside the forest. For example, she might come across a group of centaurs and have to earn their trust through her intelligence and respect for their ways.
Naruto adapts by becoming one with the forest. He observes the animals and learns from their behavior. For example, he sees how squirrels store nuts for the winter and starts doing something similar with his food supplies. He also gets used to the sounds of the forest at night, which at first might have been scary but then becomes a normal part of his life. He may even start using the natural elements of the forest like vines to help him in his ninja training.
In the fanfiction, living in the sea could give Percy a chance to explore the secrets of his water - related powers more deeply. He could learn to control the tides in a more precise way or communicate with the very essence of the ocean. He might also face challenges such as dealing with underwater magic that is different from what he's used to on land. There could be ancient sea spells that he has to decipher in order to save the sea from a dark force.
Percy could discover ancient and forgotten temples or shrines in the wild. These could hold powerful artifacts or be the lairs of minor gods or spirits. He might have to face various traps and puzzles to explore them fully. In the process, he would rely on his skills as a demigod, like his ability to control water, to overcome obstacles and uncover secrets. This would be an exciting addition to the fanfiction as it would add new elements to the Percy Jackson universe.