Eh, he's kinda got it right. Well, it seems to me that you just need to expand more around the map. The only 10 "different story lines" are just the different bosses at the end (the dots at the end of the map). So all you have to do is go to the dots you haven't played yet, you can see which you haven't played by going to Select Mode and see with boss battle is still locked. Now make your way though the Story Map in Story Mode and get to the dot. What you'll have to do is either fulfil the Dark Mission (upper dot) or Hero Mission (lower dot). There is only one Neutral Final Boss battle and that the very middle boss, Egg Dealer at Lava Shelter. It doesn't matter if you do the Dark or Hero Mission, the boss will always be the same, but I still think you have to play both missions as the endings are different IIRC, I'm not too sure.