Thanks to Lyly for the following from DocArzt.
Tonight is the night! Michaelpalooza comes to an end with the return of one of the original 815'rs. But there are a lot of questions about how and why Michael has returned. I have some hints to keep yourselves busy:
Michael's reason for returning has to deal with something he wants to do personally, but cannot do away from the island.
Despite all of my hopes and dreams to the contrary, Michael is not a clone/duplicate/ twin. :(
Michael is not being coerced to be there by Ben, but by the island itself.
An old face will reappear in a manner reminiscent of Charlie in the season 4 premiere, and (for me at least) raise some new questions about the incorporeals on the show.
Yes, yes... somebody dies... but TWO are shot.
Source: DocArzt
