Ultimate Armor X
At the title screen, press Left, Left, Left, Right, Right, Right, Left, Left, Left, Left, Right, Right, Right, Right.
Play As Alia
At the title screen press Down, R1, Up, L1, Square, X, Triangle, Circle.
Play As Layer
At the title screen press Square, Square, Right, X, R1.
Play As Pallete
At title screen press R1, X, Left, Square, Square.
at title screen press L3(2), R3, L3(2), R3, L3(2), R3, L3(2), R3.
How To Get Nightshade Zero!
At the main menu before pressing start, enter the following: L1, L1, R1, R1, L1, L1. After that go and play the game and beat it once. Then play again loading your file that beat the game and go to the place where you pick the characters. Go to Zero and press x
then it will give you options to pick Zero or Nightshade Zero.