Percy could use his water powers. He could summon water from nearby sources, like pipes or even the air if it's humid enough. With the water, he could create distractions, like water walls or waves to disorient the Avengers. Then he could make a run for it.
Well, first of all, Percy is a very resourceful character. If he was captured by SHIELD, he'd quickly assess his surroundings. Since he has control over water, he could start by causing a water - related malfunction. For example, if there were any water - cooled systems in the SHIELD facility, he could make them burst. This would create chaos and give him an opportunity to slip away. He could also use his powers to sense any water sources around, like underground water channels. He could then use these as a means of escape, perhaps creating a tunnel of water to swim through. And don't forget his sword, Riptide. He could use it to cut through any barriers or fend off agents if necessary.
Percy might try to find Voldemort's Horcruxes and destroy them. This would weaken Voldemort and give Percy a better chance to escape. He could also use his demigod speed and agility to outrun Voldemort's spells and find a way out of the dark wizard's lair.
He could use his Invisibility Cloak. The Avengers might not be able to detect it with their technology. Then he could find a way to apparate out if he's far enough from any anti - apparition charms.
Percy has his speed and agility. In the fanfiction, he might be able to use his demigod reflexes to dodge all of the Avengers' attacks. He could then quickly move in for a counter - attack. Also, his sword, Riptide, is a powerful weapon. It can cut through almost anything. He could use it to cut through the Avengers' weapons or their defenses if he gets close enough.
If Percy Jackson was captured by the Avengers in fanfiction, at first, the Avengers would likely be very cautious. They don't know his powers or his origin. Percy, on the other hand, would be scared but also defiant. He has his own world of demigods and monsters to deal with. He might initially resist the Avengers' attempts to hold him. However, as time goes on, he could start to understand their motives and they could start to understand his. This could lead to a mutual respect and a possible alliance against a common enemy, like some powerful monster from Percy's world that somehow poses a threat to Earth in the Avengers' view.
One way could be to have Percy Jackson's powers of being a demigod interact with the superpowers of the Avengers. For example, his ability to control water could be used in a joint mission with Thor's lightning powers. Maybe they are facing a common enemy that can only be defeated by combining their unique skills.
Well, in some fanfiction scenarios, Percy Jackson might betray the Avengers due to a misunderstanding. Maybe he's been misinformed about the Avengers' intentions towards the demigods. For example, if he hears false rumors that the Avengers plan to control the demigods, he could turn against them in a fit of protectiveness for his kind.
Well, Percy could use his water - controlling abilities to put out fires during the Avengers' battles. His skills with a sword could also be useful in close - combat situations against the bad guys.
Percy could fit in as a strategist. His experience in dealing with various gods and monsters gives him a unique perspective on handling threats. He might suggest different approaches that the Avengers haven't thought of before, like using the environment in a more creative way, similar to how he uses water in his battles as a demigod.
Naruto could use his shadow clones to create distractions. He could make a large number of clones and while the Akatsuki members are dealing with the clones, he could find an opening to escape. Also, he might be able to tap into the power of the Nine - Tails more than ever before in a desperate situation, using its strength to break free from any restraints.