Mega Man X: Command Mission Codes -

Axl: 38184155 or 44527839 (Japanese version)
Axl (DNA changing pose): 91327856 or 46925056 (Japanese version)
Cinnamon: 92106548 or 10950508 (Japanese version)
Cinnamon (Iron Maiden): 31415926 (Japanese version)
Marino: 02098772 or 20040729 (Japanese version)
Marino (Quicksilver): 19780506 (Japanese version)
Massimo (Dymonion): 47722361 or 82536252 (Japanese version)
Mega Man X: 73001472 or 19670801 (Japanese version)
Mega Man X (victory pose): 44162918 or 78523511 (Japanese version)
X-Armor: 19690831 or 32603260 (Japanese version)
Zero: 29290141 or 33515937 (Japanese version)
Zero (Black): 72443102 or 69203600 (Japanese version)

Unlock the Classic Mega Man:
To unlock the classic Mega Man, Finish the game. Then, highlight the "Continue" option and press (x2), (x2), , (x2), (x2), . That option will turn blue, and you can play as the Original Mega Man.

Unlock Proto Man:
Finish the game with Zero, depending on your game play. Then, highlight the "Continue" option and press , (x2), (x3), , . That option will turn red, and you will get to play as Proto man.

Hard version:
Finish the game, then highlight the "New Game" option. Then, press (x3), (x2), , . That option will turn yellow, and you will now have a hard difficulty setting.