Go to the screen where you choose your song. Press various controller buttons to display little icons on the screen that make the song do different things:

"Hide" icon

Press Red, Blue, Green, Blue, Red, Green for hidden mode. When the bars get to the middle/top area, they disappear making it very hard to hit them correctly.

"FF" icon

Press Red, Green, Blue, Pick(2) for fast forward mode. This makes the bars scroll faster.

"SFF" icon

Press Red, Green, Blue, Pick(2), Red, Green, Blue, Pick(2). The bars will scroll even faster.

"Random" icon

Press Blue, Green(2), Red, Green, Pick for random mode. Some notes will be randomized.

"SUD" icon

Press Green, Red, Blue, Green, Blue, Red, Pick at the mode selection screen. Notes will appear closer to the play line.

"Little" icon

Press Red(3), Green(2), Blue(3), Pick at the mode selection screen. This mode only allows two chords.