<(o.o)> I should probably try this game out, but I don't get why certain videos, I see the same song, but different characters and mobs in it. I didn't think the game was that diverse, just thought they used the same characters from the game the music is from..
You choose your party based off of a ton of different characters from all the games. The mobs are kinda random but often they are based on which FF the song is from. In a way it all doesn't matter too much, but the different characters adds stats into the equation which determines how fast mobs die or how much treasure you get from a song and such. Just extra little details that can make the game more fun, but in the end, not too important to the game play itself.