Tetris DS Codes -

Standard Endless mode:
Get over 200 lines to complete Standard mode to unlock the "Endless" option when selecting a level in Standard Marathon mode.

Music tracks:
Complete the following tasks in Standard Marathon mode to unlock the corresponding music track at the sound test menu.

Ancient Tetris (Tetris GB Music A): Reach level 19 
Balloon Tetris (Touch Mode Theme): Reach level 14 
Basement Tetris (Super Mario Bros. 1-2): Reach level 3 
Bowser Battle (Super Mario Bros. 1-4): Reach level 10 
CongraTetris: Complete Standard Marathon mode 
Mario Tetris 3 (Super Mario Bros. 3 Overworld): Reach level 4 
Rushed Tetris: Reach level 16 
Tetris Climber (Ice Climber Theme): Reach level 15 
Tetris DK (Push Mode Theme): Reach level 13