Alright, so, I have three memories for Gohan. (I had to work really hard to narrow this down to three.)
1. Saiyan Invasion, where Gohan (5yo) and his dad's friends have to fight Nappa and Vegeta. Originally, it ends with everyone except Gohan and Krillin dying, Krillin being incapacitated, and Gohan about to have his head stepped in by Nappa until Goku shows up. The memory will be altered to have Goku arrive too late, with Nappa having ample time to crush Gohan's head if he doesn't fight back.
2. Cell Games, while Cell is torturing Gohan (11yo) by making everyone else fight the Cell Juniors. Originally, it leads to Android 16 being killed, blinding Gohan with so much fury that he turns Super Saiyan 2. The memory will be altered to have Mr. Satan refuse to throw 16's head, leading to Gohan taking longer to transform. Which will lead to the Cell Juniors actually killing people, in the order of Tien, Yamcha, Krillin, Trunks, Vegeta, Piccolo, and Goku. This could lead to a complete mental shutdown due to trauma.
3. Majin Buu's Revival, when Gohan (18yo) and the Supreme Kai are fighting Fat Buu. Originally, it leads to Gohan being blasted away by Buu, left for dead, but ultimately still breathing. The memory will be altered to have Babidi order Buu to "play with the Saiyan", causing Buu to find Gohan, and physically beating him up with childlike glee, with no one around to stop him.
Gohan
1. Saiyan Invasion, where Gohan (5yo) and his dad's friends have to fight Nappa and Vegeta. Originally, it ends with everyone except Gohan and Krillin dying, Krillin being incapacitated, and Gohan about to have his head stepped in by Nappa until Goku shows up. The memory will be altered to have Goku arrive too late, with Nappa having ample time to crush Gohan's head if he doesn't fight back.
2. Cell Games, while Cell is torturing Gohan (11yo) by making everyone else fight the Cell Juniors. Originally, it leads to Android 16 being killed, blinding Gohan with so much fury that he turns Super Saiyan 2. The memory will be altered to have Mr. Satan refuse to throw 16's head, leading to Gohan taking longer to transform. Which will lead to the Cell Juniors actually killing people, in the order of Tien, Yamcha, Krillin, Trunks, Vegeta, Piccolo, and Goku. This could lead to a complete mental shutdown due to trauma.
3. Majin Buu's Revival, when Gohan (18yo) and the Supreme Kai are fighting Fat Buu. Originally, it leads to Gohan being blasted away by Buu, left for dead, but ultimately still breathing. The memory will be altered to have Babidi order Buu to "play with the Saiyan", causing Buu to find Gohan, and physically beating him up with childlike glee, with no one around to stop him.