In the fanfic, Naruto could receive Orochimaru's unique form of chakra manipulation. This would allow him to do things like transform his body parts into snake - like appendages for better attack and defense. And perhaps he gets the power to resist certain types of genjutsu more effectively, as Orochimaru has developed ways to counter illusions. There's also a possibility that he gets a power boost to his physical strength and speed, similar to how Orochimaru has enhanced his own body over the years.
He could have the power to instantly heal any injury. His chakra might be so vast that he can create multiple clones without getting tired. Also, he might be able to control the elements in ways that are beyond normal shinobi capabilities.
In some fanfics, Naruto might use his new and powerful jutsu that he has mastered over time. Maybe he combines his Sage Mode with the power of the Nine - Tails in a unique way that Orochimaru can't counter. For example, he could use the Nine - Tails' chakra to enhance the range and power of his Sage Mode attacks, and then catch Orochimaru off - guard.
If Naruto is brainwashed by Orochimaru, he may gain some forbidden jutsu that Orochimaru has been researching. These jutsu could be extremely powerful but also very dangerous. On the power - losing side, he could lose his ability to communicate with the spirits of the past Hokages, as Orochimaru's influence might sever that connection. His Sage Mode could also be affected. He might not be able to enter it as easily or at all, since Orochimaru's brainwashing could change his chakra nature and balance. Additionally, Naruto might gain the ability to summon different kinds of snakes, which is a trademark of Orochimaru, but this could come with the loss of his own unique summoning abilities.
Teens might receive powers like telekinesis, the power to manipulate time, or the ability to transform into different creatures thanks to the shards in the novel series. It all adds to the excitement and mystery of the story.
Perhaps in this fanfiction, Naruto has some sort of special power or transformation that he unlocks just in time to face Orochimaru. It could be related to his Nine - Tails chakra in a new and unique way. He uses this power to break through Orochimaru's defenses and save Hiruzen. Naruto might also use his knowledge of Orochimaru's weaknesses that he has learned either from Jiraiya or from his own past encounters with Orochimaru's minions.
Naruto might resist through his strong willpower. He has always been determined, and this would not change even under torture. He could keep thinking about his friends in the Leaf Village and his goal of becoming Hokage, which gives him the strength to endure.
It depends on the specific fanfic. Some authors might come up with this plot twist to explore different character motivations and conflicts. In others, it might not be the case at all.
He could be exiled from the village. This is a very severe punishment as Naruto loves his village deeply. Losing the connection with his home and friends would be a great pain for him.
A vampire in a Naruto fanfic might possess the power of hypnotism. This could be used to manipulate other characters, much like the Sharingan in some ways. They could also have the ability to transform into a bat - like form for quick movement or stealth. Additionally, they could have a regenerative ability that is much faster than normal Naruto characters, which is related to their vampiric nature.
Sephiroth might possess the power to manipulate the elements in a different way compared to Naruto characters. For example, instead of using hand signs for fire jutsu, he could summon dark - tinged flames just by his will. His power over the Lifestream could be reimagined as a connection to a different kind of energy source in the Naruto universe.