Q: So how do I beat the robot boss?
A: There's a safe spot near where the beams shoot from the left. Find the
   spot, stay in it, and fire away until the boss dies.

Q: How do I beat the eyeball thingy?
A: The safe-spot is just to the left of the eyeball. Stay there and fire
   away.

Stage select:
On the credits screen, press
Left, Up , Right, Down , Up, Right, Left, Down and then:
    Up  - Stage 2     Right - Stage 5
   Left - Stage 3    Select - Stage 6
   Down - Stage 4         B - Stage 7

Invincibility:
On the credits screen, press
A, A, Up, B, B, Down, A, B, START

Super weapons and invicibility:
On the credits screen, press
A, A, Up, B, B, Down, A, B, START
then in the game press 2x START

End of game:
When the PRESS START message appears, press
A, A, Up, B, B, Down, A, B, B, START