So what we know:
-Jacob had to eat to stay alive (i.e. the fish), plus he got knifed and kicked into the fire, so he's not invunerable, just perhaps immortal (Highlander-style)
-Jacob can travel off the island (he visited all the characters off-island)
-He knows what's going on with each character (Locke is going to fall out of a building, Kate is going to steal, etc.)
-Jacob's "buddy" can change how he looks (plastic surgery, smoke monster, morphing, whatever) and knows everything that Locke knew
-Jacob's "buddy" wants/wanted to kill Jacob for some reason
-Locke is deadsies
-Jacob sounded worried (to me at least) that "they" were coming (crew members carrying Locke's body?)
A buddy pointed out that Jacob's "friend" might also be showing himself as other people, such as Ben's daughter Alex, to prompt him to utilize the loophole to kill Jacob.
Man I really hope they have a good final series for this haha.