Well, if Goku didn't lose his memory, his relationships with his friends and family could have developed differently. Maybe he'd have fewer conflicts or approach problems with a clearer mind.
If Goku never lost his tail, his powers and abilities might have developed differently. Maybe he would have retained some primal monkey-like traits that could have given him unique advantages or disadvantages in battles.
Well, Goku's power level progression could be different in that he might be more in control of it. Since the head injury had some impact on his psyche, without it, he could have a more calculated approach to increasing his power. He might not rely as much on the Kaioken technique, which was developed in part due to his need to overcome limitations caused by his injury - affected development. Instead, he could focus more on pure Saiyan power - up methods like the Great Ape transformation and evolving it further.
It was a Chinese idiom, meaning to mix together and describe an extremely chaotic situation. This idiom came from Lu Xun's "Hot Wind·Random Thoughts Record Thirty-Three". It is often used to describe the chaotic state of things or situations. Chaos also appeared in the titles and authors of some novels, but the specific content and background information of these novels were not provided.
One possible plot could be that Goku's power development takes a completely different path. Without the head injury that altered his original Saiyan nature in the official story, he might be more in tune with his Saiyan instincts from the start. This could lead to him being more aggressive in his battles and perhaps having a different moral code when it comes to fighting. He may not have the same innocent and somewhat naive view of the world that he had in the original story, which was partly shaped by his head injury.
Perhaps in this fanfiction, Goku remembers all his past battles vividly. This could lead to him having unique strategies against old foes. For example, when facing Frieza again, he recalls every single move Frieza made during their previous encounters and is able to counter them with ease, making the fight much more one - sided in his favor.
If Goku never hit his head, he might not have become the kind-hearted hero we know. Maybe he would have remained a fierce warrior focused only on power and conquest.
A complete mess was an idiom. It meant that the scene was chaotic, things were scattered all over the ground, or it described the chaotic state of things. This idiom originated from Zi Zhi Tong Jian. It described the turmoil in the country at the end of the Tang Dynasty. The warlords fought in various places, causing the people to be displaced and the society to be chaotic.