Well, he could change a lot of things. Maybe he'd prevent some bad events from happening in the past. For example, he could stop Frieza from destroying Planet Vegeta earlier. It would be really cool to see how his super saiyan power affects the past timeline.
Well, he might change some crucial events. For example, he could prevent some villains from ever rising to power. Maybe he'd stop Frieza from destroying Planet Vegeta earlier, which would change the whole Saiyan history and his own life. He could also teach his past self some new techniques, making the Saiyans even stronger in that timeline.
If Goku travels back in time as a Super Saiyan in fanfiction, his relationship with his past self would be complex. His past self might look up to him as a hero and a mentor, but at the same time, there could be some envy or confusion. With his Saiyan comrades, he could become a leader figure much earlier, changing the power dynamics among them. Also, his interactions with Earthlings would be different. They would be more fearful or more in need of his protection, depending on how he uses his power in the past.
In this fanfiction scenario, Goku could meet Bulma when she was a child. He could befriend her in a different way compared to their first meeting in the original story. Also, he could run into King Kai at an earlier time and start training with him much sooner, which would significantly boost his power levels and change the course of his battles in the future.
Well, perhaps Goku travels back in time to meet his long - dead parents. He could have conversations with them, learn about his family's history in a more personal way, and gain new insights that help him in his present - day battles. Or he might go back to the time when the Saiyans were still on their home planet, and try to change the fate of the Saiyan race by warning them about their impending doom.
Goku might run into past versions of his friends. He could see a younger Krillin or Bulma and have some really interesting interactions. He could also meet past versions of his enemies and try to change their fates. For instance, he could meet a young Vegeta and try to steer him away from the path of evil. This would be a huge change in the Saiyan's story.
She could meet the founders of Hogwarts. Imagine Hermione having a conversation with Rowena Ravenclaw about the importance of knowledge and wisdom. She might also meet Godric Gryffindor and learn about the true meaning of courage from him. Another person she could meet is Salazar Slytherin. It would be very interesting to see how she would interact with him, given his views on blood purity.
Frieza would be a great antagonist. If Goku goes back in time to a point before Frieza was defeated, Frieza could be an even more menacing force as Goku might not have all the power - ups he had in the original timeline. He'd have to rely on his wits and basic training more.
In some cases, the antagonist could be Esme herself, or rather a version of her from the past. The past Esme might be more naive or self - centered and not understand the implications of Esme's actions in the past. The present Esme is trying to make positive changes, but the past version of herself keeps getting in the way, either through her own actions or by influencing the people around her in a negative way.