TMIB= the man in black/locke

So, the "core" of the island is basically what gives jacob and his successors, as well as the TMIB, their "power." When it is active, TMIB cannot leave the island and cannot kill the successors, while he cannot be killed himself. However, with desmond taking out the core thingy, TMIB pretty much becomes human and can be killed, but can also kill the successors. Jack and him fight, w/e, and jack kills him.

However, without the core of the island where it was, the island will collapse. TMIB's plan was to flee the island before that would happen, and before he was killed. Jacob, however, had another plan, which was to kill TMIB while the stone was out, and replacing it, thus ridding the island of many of its problems and all that. JAck, by replacing the stone, stops the island from destroying itself.

Hurley, Ben, and Desmond are now the only ones left on the island at the end of the whole shebang, and we never really determine if desmond lives through it. Hurley is now the island's protector, and he and ben decide to protect it together.

The whole alternate timeline actually turns out to be "purgatory" (ironic, since many fans thought the island was purgatory a while ago) Where all the members of the island are supposed to meet again and move on. Each member, when reunited with a lover, gains their memory back and realizes they're dead, with the exceptions of Jack, Hurley, and Desmond it seems. Desmond says int he normal timeline that he would go to a different place after moving the core of the island, which may explain why he didnt need to connect with anyone to gain back his memory. Hurley could be accounted for because he was the protector of the island, and Jack was only different in that it was his dad's coffin.

Also funny, was the moment Sun and Jin gained their memory back, thinking back on it, it made sense that they were like "we dont need protection" lol. The clues were there from the beginning actually. We cuda guessed it

TL;DR The island is not purgatory. Jack needs to move teh stone back and forth to kill the smoke monster and save the island. Alternate timeline is purgatory, after they're all dead. They find peace and move on.

Many things, however, still weren't answered, although a lot could be reasoned. Like, the fact that the others couldnt have children could be attributed to the large amount of Electro magnetic radiation they recieved from the core of the island. It was also confusing as to what jacob had done. They hint that he had put in measures to stop people from leaving and coming back to the island, but they also said it could be changed. The "time shift" effect could ahve just been caused by the electro magnetism messing with computer systems, etc.

But the polar bears? C'mon, that still makes no sense.