In the fanfiction where Sam goes back in time, what changes occur?

Well, usually there are big changes. Maybe they prevent some tragedies or fix past mistakes that affect the future.

Well, there could be all sorts of changes. Maybe he'd get a chance to fix past mistakes or prevent certain events from happening.

Well, in some fanfictions, they go back in time and accidentally interfere with the lives of their younger selves. This creates all sorts of chaos as they have to deal with the younger Sam and Dean's reactions to seeing their future selves. Or perhaps they go back to a crucial moment in the history of the hunter community and end up changing the rules and relationships within it. It could also be that they go back in time to a specific era like the Wild West and have to deal with supernatural threats that were prevalent during that time.

He might have trouble adapting to the past and avoiding changing events that could have unforeseen consequences.

One plot idea could be Sam going back in time to prevent a major tragedy in his family's past. For example, he could try to stop the demon from killing Mary Winchester, which would change the entire course of his and Dean's lives. Another idea is that he goes back to a time when hunters were just starting to organize and he tries to influence the development of the hunting community for the better.

The main characters are Sam and Dean Winchester, of course. But in some fanfictions, Bobby Singer might also be involved. Since he was like a father figure to them, he could be the one guiding them through the time - travel process, or he could be there in the past waiting for them. Also, the characters of their parents, Mary and John Winchester, might show up if they go back to a time when their parents were alive.

He could meet his grandparents. Meeting them would give him a deeper understanding of his family history and the roots of the Winchester family's connection to the supernatural. Another interesting character would be young John Winchester. Sam could see what his father was like before all the tragedies happened and maybe even influence him in a positive way.

She could meet her younger self. This would be an interesting encounter as she could offer advice and guidance to her younger version. Maybe she could help her younger self to be less afraid of her powers.

Winston undergoes a significant transformation. He becomes more resigned and less rebellious against the system.

One change could be in the strategies used in battles. Older Ruby has more experience, so she could introduce new fighting techniques to her younger self and the team. This might give them an edge against their enemies. For instance, she could show them how to better use their weapons in combination with their semblances.