Final Fantasy Crystal Chronicles: Echoes of Time Unlockables

Get all the events in the Library, then go back and clear the enemies in the first area. This will unlock a warp point that takes you to where you can fight the bosses from Final Fantasy Crystal Chronicles: Ring of Fates. Place the book on the bookstand to fight.

First you have to beat the boss once, then you can go back and find a warp point that will take you back to that boss so you can fight the battle again.