Taiko no Tatsujin DS: Touch de Dokodon!
Complete twenty songs to unlock the Oni difficulty setting.
Complete thirty songs. Then, go to the Song Selection
screen and press Down/Right to display the options. The
Perfect mode icon resembles a yellow Don wearing a gold crown.
In Perfect mode, one missed note will result in a failed song.
Complete thirty songs. Then, go to the Song Selection screen and press Down/Right to display the options. The High-Speed 4 mode icon resembles an animal with an open mouth with a red flag next to its name. In High-Speed 4b mode, notes will scroll four times as fast.
To unlock songs normally, you must use the Daily Training Dojo once a day. To do this quickly, change the system date to the next day after you are done and repeat until all six songs are unlocked.
Strategy guides from GameFAQs