Extra Mode:

On the Title screen, hold Select and press Start to access the Options screen. Then, press and hold R and enter the following: simultaneously press Up and X , Then Right and A, then Down and B and finally Left and Y. If you enter this correctly, the screen will switch to the Extra Play Mode. Use the Control Pad to change options.

 

Infinite Credits:

Enter the following code at the Title Screen:

Hold Select then Hold Start, release Select.

Then at the Options Screen Hold L and Press Up + X - Left + Y - Down + B - Right + A then release L.

Doing this correctly will give you infinite credits