MX was a floating heart for two seconds, yet Nomura clarified that he wasn't a Heartless. XH is virtually the same thing that MX was.
Not classified, most likely because his darkness wasn't surrounding it, but essentially. After all, MX said he has returned a complete person, yet he looks like his old self. Master Xehanort disgarded his body and soul to claim Terra's. Xehanort seems to have done the same.
Heartless are normally mindless and emotionless. Because Xehanort(If I understand things correctly), released his heart via Keyblade and KM title. he never really lost his sense of self, and so his memories never transferred to Xemnas.
Ansem Report 12: I have transcended to an existence of only the heart. I should have come back as a Heartless, but there is no sign of such a transformation.
My body has surely perished. However, I am different from the other Heartless, keeping the memories of before, and I have not taken on the form of a Heartless.
It is evident that there are still many things to be studied.
In order to cross over to the dark realm, which is not this world, you must go beyond the door of Kingdom Hearts, the heart of all worlds.
The core connected to the world's heart, the place that will take me to the world of darkness. (I will record the details in another report...)
There are still so many unknown worlds.
The Realm of the present...The Realm of Darkness.
The Realm of Light.
And, The Realm of In-Between.
In which one does true paradise lie, I wonder?
Secret Ansem Report 10: Sora went to sleep in order to recover the memories he had lost in Castle Oblivion. It would take quite some time to bring back all the memories he had created in his lifetime.But Organization XIII held sway over Castle Oblivion. Sora would need to be kept someplace more secure.I persuaded Naminé to move the slumbering Sora to Twilight Town for safekeeping.Naminé.
As I have written before, she is a most unusual being.Born of the same process as a Nobody, but lacking virtually all the elements of a Nobody.Perhaps she continues drawing in hopes of capturing that which she lacks: the memories of others, especially Sora.
I have arrived at a hypothesis.
I believe that Naminé was born as a special type of Nobody when Sora attacked himself with the Keyblade, causing his and Kairi's hearts to leave their bodies simultaneously.Naminé emerged as Kairi's Nobody...but the body and soul necessary to exist as a Nobody belonged to Sora.When a person's heart is stolen, a Heartless is born with no sense of self, and the body and soul left behind give rise to a Nobody.
But what if one willingly releases one's heart from one's body?
Sora and Xehanort retained their selfhood even after becoming Heartless.
Then there are Kairi and Naminé.
Kairi was exceptional for having had no darkness within her heart. Also exceptional was that her heart, once freed, migrated to a new vessel—Sora.
The combination of the two theoretically unlikely exceptions may be behind this anomaly.
There are matters I must attend to while Sora is sleeping.
A new ally has appeared on the scene: Riku.
Much like with XH, it seems the recompletion process has changed, rather corrupted the appearance of Terra's body to look that of Master Xehanort.
It seems as though the most recent version of Xehanort(MX) will not be the main focus in the struggle to save Terra.