Complete the game once and save. At the title screen select "new game," press and hold the L shoulder button and press start. There will be a second chime. When the game starts zero will be in the Protoform (dark green armor).
NOTE: Forms and EX skill can not be earned in hard mode. Also, your weapons will not level up.
Beat hard mode
Highlight newgame.
Press and hold the L and R shoulder buttons and the select button.
Press start. You will hear a second tone and be taken to the first image in the gallery.
While viewing images, press select to view/hide the image title.
Some images can be scrolled up or down using the d-pad.
Press start to exit to the title screen.
Perform these tasks in a level to unlock Zero's other forms: