The entity is unfamiliar with human beings, and underestimated the level of pain ripping you open to sew on new features would cause. Your mind can't take it. You feel your consciousness drift out of physicality, and while you remain alive, you are a shell of the person you once were. Your mind is being rewired to fit with Riley's wish. You will no longer be their friend. You will no longer be you. 

But! on the bright side, you have gotten your wish too! Rich, talented, and charismatic! Too bad it feels like you are playing a character in show, rather than playing yourself.