Should Auld Acquaintance...G 10

Enter the Konami code at the main menu (where it has you choose what mode you're gonna play).

Up, up, down, down, left, right, left, right, B, A


If you enter the code too fast, it may just send you back to the press blah blah blah to start screen.


If you want the achievement without using the code for some reason, 1999 Mode is unlocked after completing the game for the first time.