It could be one of Sonic's old enemies who found a way to transform into him. Maybe Dr. Eggman created a sophisticated robot that looks and acts like Sonic.
In this fanfiction, it might be a new character. This new character could be jealous of Sonic's popularity and decides to take over his identity. They might have studied Sonic closely and learned his mannerisms to be a convincing imposter. Another possibility is that it could be a character from an alternate dimension who accidentally or purposely switches places with Sonic and then tries to keep up the act in Sonic's world.
There are several candidates. A power - hungry villain who wants to rule Sonic's world by taking his identity is a likely option. It could also be a shape - shifter who just wants to have some fun at Sonic's expense. Or perhaps a character who was wronged by Sonic in some way and is seeking revenge by replacing him and ruining his reputation among his friends and the inhabitants of his world.
Look to Chapter 31 for the clearest answer. It begins with Before Shen Lan had reached the backyard, she already heard the sounds of..., keeps building through Facing the freshly risen morning sun, she noticed at a glance the girl..., and lands on After staying in the study and reading for another.
Chapter 826, "Deadlock", is the clearest early answer because the violence around Shuiyun Temple becomes final instead of hypothetical.
The best chapter pointer here is Chapter 37, "Those in the know anticipate the transformation, while the oblivious think it's a fashion show.". It opens with The barrage was suddenly filled with hahas, but the two guests present...
A practical answer is Chapter 13, because it turns the idea into a concrete scene. The chapter opens with Sensing that something was off with Jiang Yan, Jiang Yan dismissed the..., adds pressure through He probably had a good guess who it was., and ends on How could this happen..." Lin Manru.
Chapter 920, "College Entrance Exam Results Inquiry", is the clearest early answer because it turns Meng Xuezhi's situation into a concrete plot event. Early on, Outside the nursing home, Meng WanZhi anxiously waited in the car for....
Chapter 709, "But He Really Is My Second Uncle", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from The voice came from Jiang Li.
The best chapter pointer here is Chapter 3, "Madam, the eldest young master has been missing for over half a month". It opens with Qiao was still annoyed at the attitude of this unknown girl when she heard... and closes on Jiang Yan, forced into a marriage with someone he did not love, had....
A practical answer is Chapter 14, because it turns the idea into a concrete scene. The chapter opens with Lin Manru had a rare good night's sleep., adds pressure through The young, vibrant life was buried amid the vast expanse of white, along..., and ends on But clearly, Lin Manru was unable to.
Chapter 788, "Don’t be so fierce, I'm scared", is the clearest early answer because it turns Don's situation into a concrete plot event. Early on, Song Xue covered her mouth in shock.. By the end, I really did not push the auntie that day; maybe the living room....
Look to Chapter 3 for the clearest answer. It begins with Qiao was still annoyed at the attitude of this unknown girl when she heard..., keeps building through She's actually Miss Jiang Li from the Jiang Family?!, and lands on Jiang Yan, forced into a marriage with someone he did not love, had....