When the music stops at the title screen. Press down, A, and B at the same time. You will hear a sound if you did it right. If you press it 6 times you will see the end.
At the title screen, hold Down on the D-Pad and press A + B simultaneously; you'll hear a chime to confirm, but the music may not be very loud so you will have to listen carefully. If you do this once, you'll start at Stage 1 with invincibility. If you enter the code several times, you'll start at different stages, depending on how many chimes you hear(2=Stage 2, 3=Stage 3, etc.).
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