The theories section has been pretty stale lately and since we're at the end, I'm just putting this here instead. After watching 'Across The Sea', I'm convinced that the light and water is what will be used to trap or kill MIB. Jack will become the protector of the island and will lead Desmond to the light cave. Desmond will somehow be able to use his unique abilities to sink the island, trapping MIB. Then, although many here have dreaded the thought, the ATL will be the 'happily ever after' reward for all the hard work and sacrifice everyone endured.
Along the way, we may also see Jacob's ashes being used to contain MIB so that this plan can be played out. And I think we will also be shown that the whole purpose of containing MIB is because if MIB leaves the island, the balance of light and dark will be disturbed, the light will be extinguished, and life everywhere will cease to exist.
That's it, I think I'm done thinking until next Sunday, my head hurts and my nose has started bleeding!
