This is what I thought:
Jacob's brother's persona and soul was separated from him and merged with the light creating "the monster". Now, the light is represented under a real conscious and persona (of Jacob's brother).
Then I talked to my friend. And he thought:
The monster is its own persona. Not his brother's. And the monster wants to leave too, and can take forms of people, but once it does, it is affected by that person's memories and character.
So what do you think? MiB's persona in the form of black smoke and light, or black smoke is completely different thing that wants to leave too.
I'm going with he first one.
And my theory:
The island sunk in the FST because the MiB left, and without the light on the island, it "deflated" and sunk.
Which is maybe how the show ends. Maybe the MiB will try and kill himself and release the light, sinking the island?
Or he will be separated from the light and smoke, and that will go back to the cave, and the MiB will get to leave. Happy ending :)
What do you think?