During the opening before the title screen. Very classic button combinations.

Effect                                    Code
-----------------------------------------------------------------------
Big Head Mode                           - A, B, A, Y, A, B, B	
Blue Screen Of Nerd: gives you a laugh. - Up, Up, Down, Down, Left, Right, Left, 
                                          Right, B(fire), A(jump)	
Hedgehog Mode: run like the fastest 
thing alive.                            - Up, Down, Left, Right, A(Jump)