For these codes to work, you must press the buttons during gameplay, but NOT paused:

All Weapons – Left, Right, Left, Left, Right, Left, Right, Right, Up, Down, Up, Up, Down, Up, Down, Down.

Invincible – Left, X, Left, X, Left, Left, X, Right, X, Right, X, X.

Level Codes

level 1       circle,circle, circle,circle, circle, circle
level 2       square,X,square,X,triangle,square
level 3       triangle,square,square,circle,circle,triangle
level 4       triangle,square,triangle,triangle,circle,triangle
level 5       square,triangle,triangle,triangle,X,triangle
level 6       triangle,square,circle,circle,X,square
level 7       X,square,square,square,circle,triangle
level 8       triangle,square,X,square,triangle,triangle
level 9       square,triangle,square,X,triangle,X
level 10      triangle,triangle,circle,square,X,square
level 11      triangle,triangle,X,triangle,circle,square
level 12      circle,square,triangle,triangle,triangle,circle
level 13      triangle,square, circle,X,triangle,square,
level 14      triangle,triangle,X,square,square,X

level 15      circle, x, triangle, triangle, triangle, triangle
level 16      circle, square, circle, circle, circle, square
level 17      triangle, triangle, triangle, circle, triangle, square
level 18      square, circle, square, x, square, triangle
level 19      x, x, square, x, triangle, circle
level 20      x, square, x, triangle, triangle, squar

Thanks to Revolution readers Aidan Reilly-Seivert, adam johnston and Hebro!