He could gain the ability to create large - scale wooden structures, like Hashirama did. For instance, he could build huge wooden golems to fight for him in battles.
He might gain the ability to manipulate ice like Haku. This could be a very useful addition to his existing skill set, especially in battles against fire - type opponents. He could create ice clones instead of the regular shadow clones, which would be more durable in certain situations.
One common theme is the discovery and acceptance of the mokuton bloodline. Often, the characters start off not knowing they have this power or are afraid of it. Another theme is the struggle for control. Since mokuton is a powerful ability, characters have to learn how to control it without it getting out of hand.
Mokuton in fanfiction is sometimes depicted as a gift that comes with great responsibility. The characters with this power often have to learn to control it to avoid causing chaos. Regarding the Iron Bloodline, it's often associated with a certain lineage in fanfictions. It can bring out different aspects depending on the author's interpretation. Some fanfictions show it as a power that can be awakened under extreme stress, and when combined with Mokuton, it can create some truly unique and overpowered abilities.
He probably gains the ability to control the chakra of the Kyuubi more freely. This could mean enhanced strength, speed, and reflexes. He might also be able to use some of the Kyuubi's unique jutsu like the Tailed Beast Ball. His healing factor could be improved as well, allowing him to recover from injuries faster.
Well, it could have the ability to manipulate time on a small scale. For example, the user could slow down time for a brief moment in battle, giving them an edge to dodge attacks or land precise strikes. This would be a really cool and unique ability compared to the existing bloodlines in the Naruto universe.
Naruto would gain super strength. He could lift extremely heavy objects with ease, like mountains or large buildings in the Naruto world. He would also have super speed, enabling him to move faster than any ninja technique. And of course, he would be able to fly, which is a completely new ability in the Naruto universe.
Naruto could gain the ability to manipulate light and darkness, which are often associated with Keyblades. This would be a huge change from his normal chakra - based abilities. He could also use the Keyblade to fly, giving him an advantage in both mobility and combat. Another new ability might be the power to heal, as some Keyblades have restorative properties.
Naruto might gain superhuman strength like Kratos. He could easily break through solid rock or lift extremely heavy objects. His speed could also increase, allowing him to move so fast that enemies can barely see him. Maybe he could also have the ability to summon the blades of chaos, which he could use in combat in a unique way, like combining them with his kunai.
Naruto might gain the power of shikai and bankai. Shikai is the first release of a zanpakuto's power, and bankai is the ultimate form. Naruto, with his determination and strong will, would strive to master these forms. Shikai could give him new attacks and defenses, while bankai could make him an extremely powerful force. For example, his bankai could combine his ninjutsu skills with the zanpakuto's power in a unique and devastating way.
Naruto could potentially gain the power of omnipotence. Since the Infinity Stones are extremely powerful in the Marvel universe, in the Naruto fanfiction, they could give Naruto abilities beyond imagination. He might be able to use the Stones together to rewrite the rules of the ninja world. For example, he could make chakra obsolete and introduce a new form of energy using the combined powers of the Stones. Also, he could use the Power Stone to boost the power of his Rasengan to an unimaginable level, capable of destroying entire mountains with a single throw.