Theatrhythm Final Fantasy/Chaos Shrine

After playing the other two modes, you will receive a Dark Note, and will be able to play Chaos Shrine mode. This unique mode tends to grant less Rhythmia than other modes, and high scores are not recorded, but it makes for it by granting lots of experience points and items.

Dark Notes
Dark Notes are random combinations of one FMS and one BMS. The exact songs are only revealed after beating them, so new notes are a challenge. Furthermore, aspects of a song, including difficulty, are randomized and constantly change throughout the song, so this mode in general is more erratic than Series and Challenge.

There are three bosses for every Dark Note. Your characters' stats and your performance will determine which boss you meet.

After the initial unlocking of Chaos Shrine mode, Dark Notes can be unlocked by beating an existing note for the first time or by trading for one in StreetPass.