Although Sonic does carry a specific personality, it's important to note that emotions and any human-like traces work very different on them, since they are not a physical entity and exist in another dimensional realm, so take this as a "translation" of their personality to a closest language. With that said, Sonic's personality will slowly transition during a game's playthrough, as they get progressively more aware of what they are and their true potential. At core they have an eccentric personality, they have a big ego and are very manipulative, being extremely clever. They hide their true intentions from their victims, luring them with something that they like and/or is special to them, trying to come off as welcoming & comforting, creating a false sensation of safeness and masking their true core in the simulated personality of the character they are impersonating. Although being a formidable liar, they can get very angry when things don't go the way they intended, in those instances, they have a hard time hiding some of their true aspects.
This leads to their whole world getting unstable together with them, since Sonic, is not only the character, but the whole anomaly and everything in it. In those circumstances Sonic might have very rapid mood changes and turn into the Midareta form, In this state, he becomes in-between no self-awareness and full self-awareness, which results in instability and inexpressibly "feeling gray". This is a very unstable form that affects not only Sonic, but their surroundings too. After obtaining the third ring, Sonic takes the Wurugashikoi form, in this state, he becomes fully self-aware himself, as they can bend the anomaly to their will without limits and even affect the real world. They no longer try mimicking the original Sonic mannerisms and instead take on a more eccentric and confident posture, which reflects their narcissist and sadistic nature a lot more.
When Sonic's true nature leaks through to the point where their model starts to alter drastically, he then assumes his Kyokai form. Despite being closer to their "true form", it cannot be fully conceived in 3D, so the model collapses in on itself, giving Sonic a broken mesh appearance. The rings are fused into his body and becomes massively taller. Sonic is incapable of true love and the only thing that truly matters to them is their goal, they have zero moral code, (ran out of space and will post more rewrite lore