At the main menu, press L1(3), R2. If you entered the code correctly, you will hear a sound. Start a new game and find Revived Hunter. He will be in Dark form.
Easy attack with Zero
Press Attack + Dash continuously with Zero.
Play as Zero
Find Zero with the teleporters and fight him. He will join you after he is defeated.
X's Ultimate Armor
At the main menu, press Left(3), Right. If you entered the code correctly, you will hear a sound.