The Variable is Daniel Faraday
As soon as I saw that Lost’s 100th episode was titled “The Variable” my mind immediately focused on Faraday. While a constant represents a value that is unchanging a variable represents change. This is why I think that the newly returned Faraday came back because he has figured out a way to change time. Now this would apparently violate the whatever happened happened rule, but what if time changing was always what happened? I know that seems a little nonsensical but what if events like the purge occured due to Faraday changing time, it follows that this change in time was what always happened. Another piece of support for this theory is the timeline map that Ceasar finds in “the life and death of jeremy bentham”. There’s a distinction between real time and various other extrapolates of an over-arching time line. So maybe the over-arching timeline includes a change in a subset timeline.
So I was thinking what exactly Faraday would do to change time and I ended up thinking of jughead. In the episode he asks ellie to bury it because “50 years from now this island is still here”. So jughead was buried and stayed that way for 50 years, maybe Faraday will attempt to change this fact. Feel free to share you opinions.