So is essentially asking who would win between Lucifer and a person whose power is to mimic Lucifer? And not just their powers either, as then it could be argued that the character would win by virtue of having more experience with their powers. It seems like Fictional Mimicry can mimic any and all traits of a character, including their proficiency with their powers.
So basically it's who would win between the character and a person perfectly copying the powers, skills and other attributes of the character. So it's a tie, surely? It would seem to be equivalent in practice to pitting the character against themselves.