I myself come into form as an INTP.
First off, let me clarify a few things with my own two cents.
The MBTI, while not completely without merit, does have its own flaws to boot.
I.E: The fact that the sixteen types here are not "true" personality types per say, rather they list the order order of your preferred congitive processes. An example would be for the INTP is that they utilize their intuition, thinking, and perciving functions more often than their tertiary ones. In other words, they are means of processing information. It shoudl also be stated that every individual has their own quirks about them that makes it difiicult to completely pin anyone under some said personality type, fictional characters especially so.
To me, personality is composed of elements of one's character where both static and dynamic traits exists.
Though I do find myself without fail to be an INTP, I most certainly exhibit traits from the INTJ Luna, with her description also fitting me to a point. Ex: As a gamer in multiplayer games such as Red Orchestra, I usually take the helm of being the leader, making quick and decisive descisions in the heat of battle. I also display an excess of both cynicism and pessimissm, as users on FimFiction can attest to in spades. Outside of gaming, I usually go back to a more INTP mode of operating. It usually depends on the situational circumstances at any given moment.
Overall, it is my opinion that in the MBTI system, we each have a "main" so called personality type, such as with me mainly operating as an INTP. Similarly to the Ennegramn Personality Sorter however, I also sometimes shift into "sub types", exhibiting both functions and traits both active and passive from both the INTJ and the ISTP.
Fictional characters are especially prone to shifting their personality types if one is to use the MBTI to type them, due to them being character's whose personality may shift according to the whims of the writers and requirements of an episode. Twilight Sparkle is a mix of being an INTP, INTJ, and ISTJ, with the closest thing that could be called a "main primarily type" being that of the ISTJ. In season 1, she displayed a mostly prominent INTP type of function. Season 2 and onward would be a mixture of INTJ/ISTJ.
My apologies for the ramblings. I myself have difficulty in wording my ideas coherently most of the time.
Hopefully this adds a littl eto the discussion. I may have more to elaborate on as time goes by, so stay tuned for further updates.