Some of them might be excited. They could see new ideas and interpretations of their world that they hadn't thought of before. For instance, if there are new bending techniques in the fanfiction, the benders in the gaang might be eager to try them out in their imagination. Others might be more critical and point out inaccuracies compared to their real - life experiences in the Avatar world.
Well, they might be really surprised. They could find the new characters and different storylines in the fanfiction quite fascinating. Maybe they'd be a bit confused at first, especially when the fanfiction takes some creative liberties with their own world and characters. But overall, it could be an interesting experience for them to see how fans perceive their world and adventures.
Korra would likely be very cautious at first. She's used to dealing with powerful opponents, but Hollow Ichigo's otherworldly nature would be something new. She might try to communicate with him, but if he showed aggression, she'd be ready to fight. Asami would probably be more strategic, trying to figure out his weaknesses. Mako and Bolin would be a bit more intimidated. Mako might use his lightning - bending as a first line of defense, while Bolin would be thinking of ways to use his earth - bending to either trap or slow down Hollow Ichigo.
Some of the gaang members might be very excited. Aang, being the Avatar, would probably be curious to learn from Ursa. He could ask her about the Fire Nation's history and how it relates to the balance of the world.
One interesting fanfiction could be 'Time's Echo'. It beautifully weaves the story of Korra and the Gaang through time. The author manages to keep the characters' personalities intact while exploring the time travel concept. Another great one is 'Gaang's Time Adventure'. It has a lot of exciting plot twists as the Gaang meets Korra in different time periods.
They'd probably be shocked. Zuko's past is full of hardships and they might not have expected all that he's been through.
One interesting plot point is the clash of different time periods' cultures. For example, when Korra, from a more modern - ish world in 'Legend of Korra', meets the Gaang from a more traditional 'Avatar: The Last Airbender' era. Another is how the bending abilities might be affected or enhanced by time travel. Maybe a character discovers a new way to bend because of the time - travel anomaly.
Ask other fans of the show in online forums or social media groups dedicated to 'The Legend of Korra'. They might be able to recommend some really great fanfictions that they've read. You can also follow fanfiction authors who are known for writing good 'Legend of Korra' stories.
Yugo could fit in as a unique foreigner. His Wakfu - based powers would be a new and strange concept in the Legend of Korra world. He might initially be seen as a threat because of his unfamiliar powers, but as he shows his good intentions, he could be accepted. For example, he could use his powers to help Korra in her fight against the Equalists, as his abilities could provide an unexpected advantage against their technology - based attacks.
They would probably have a lot of discussions. Aang might start by asking others what they think about a particular fight in the fanfiction.
One good experience could be finding fanfictions that expand on the relationships between the characters. For example, those that explore the friendship between Korra and Asami in more depth. It gives a new perspective on their bond.