There is a room in Mouna Temple after you save the void maiden that has about 9 blob creatures in it. Work your way to it and equip the great oar, use its latent power to destroy them all exit the room then re enter and repeat. 650 xp each time. expiriment with ways to destroy the blobs.
Rescue all 28 Mystics before completing the game. Proceed to finish the game and make a clear game save. The Jukebox will be unlocked and can be accessed on the title screen under the new 'Extras' category.And there it is all the soundtrack
Beat the game once and save the clear data file then load it to unlock Hard Mode.