One possibility is that his return is not as straightforward as it seems. There could be some side - effects from wherever he was. He might struggle with his identity, like he's not sure if he's really the old Wally or if he's been changed in some fundamental way. And the team would have to help him figure it out while also dealing with the fact that he's back and what that means for their dynamic.
Well, it could be that Wally returns with new superpowers. Maybe he was in some sort of time - warp or alternate dimension and comes back stronger. He might have to prove himself to the team again that he's still the same Wally they knew.
Perhaps he returns with a mission. He could have learned something crucial in the place he was away. For example, he found out about an impending threat to the Young Justice team or the world. So he comes back to warn them and help them prepare for it. And he has to adjust to the changes in the team during his absence as well.
Maybe Wally returns with new superpowers. He could surprise his old friends in Young Justice and they all go on a new mission together.
In a 'Young Justice Outsiders Wally Returns' fanfiction, he might return as a changed person. He could have lost his memories while away and slowly regain them as he interacts with his old friends. His return could also bring back old threats that were thought to be gone. For example, an enemy from his past might resurface, believing that Wally holds the key to something they want.
Wally could be developed by showing his growth in character. For example, if he was a bit cocky before, he could return more humble and with a deeper understanding of the world. This change could be a result of his experiences while he was away.
One idea could be that when Wally returns, he has new superpowers. Maybe he gained the ability to manipulate time during his time away, which he has to learn to control. This could add a whole new dynamic to the team as they deal with the implications of such a powerful ability.
Maybe a villain from the dimension where Wally has been. This villain could have followed Wally back to seek revenge or to take over the world that Wally has come back to. Since Wally has some knowledge about this villain, it would be his responsibility to stop the villain and protect his friends and the world. The villain might have powers that are a match for Wally's, making it a really tough fight.
It could be a new villain who has a vendetta against speedsters. Since Wally is a speedster, this villain might see his return as an opportunity to prove himself. Maybe he's a scientist who has developed a weapon specifically designed to counter speedsters' abilities.
One great 'Great Wally West Young Justice' fanfiction is 'Speedster's Redemption'. It delves deep into Wally's character, exploring his growth after facing some tough challenges in the Young Justice universe. The author does a wonderful job of capturing his voice and the relationships he has with the other characters.
One great fanfiction could be about Wally West getting some unexpected training from Doctor Fate. Maybe Fate sees potential in Wally's speed and decides to teach him some magic - related skills to enhance his combat abilities. This could lead to some really cool adventures where Wally has to combine his super - speed with new magical powers.
A plot could be that Wally is cursed by an ancient magic and Doctor Fate is the only one who can break it. So, Wally has to follow Doctor Fate's instructions and training to get rid of the curse. Along the way, he discovers new aspects of his powers and also about the magical side of the Young Justice universe.
Well, 'Speed Force Adventures of Wally West' is an exciting fanfiction. It shows Wally using his speed in really creative ways during Young Justice missions. 'Wally and the Team' is also a good one. It's about how Wally interacts with different members of the Young Justice team, like his banter with Robin and his mentorship - like relationship with some of the newer members. And 'Wally's Time - Out' is interesting as it explores a period where Wally has to take a break from heroics and how he deals with it.