Turn on the game, go to the Option Screen, then press CNTRL I: B Y Y Y B Y Y Y START. Begin a new game and you will begin on the first Bonus level.
Go to the Option Screen and hold down [R] [L]. The Credit Screen appears, where you can press SELECT to view the different backrounds.
Warp to Level 11:
In the Options Screen, press Bx8 and a tone will sound. Press START and return to the Title Screen. Begin a One-Player game; you will begin on level 11.