Wow people did some major posts here. But i think i would like a try at explaining the Tidus situation. In FFX when Tidus is first learning about being a dream of the fayth, the fayth talking to him says that Tidus, and his father, are no longer dreams, they are more then dreams (some jazz like that). This seems to be pointing towards Tidus being alive in some way or another so when he faded away at the end of ffx he just died and went to the farplane. In ffx-2 the fayth brought Tidus back by either dreaming up a new body for him to live in, created one with pyreflies, or maybe they an organic body soemhow.