Successfully complete the game. Select the "New Game" option and you will be able to select an alternate costume for Enoch. To unlock the alternate costumes, complete the following tasks.

Achievement	How to unlock
Dark Enoch	Complete Chapter 8 with an "A" or better rank.
Old Armor A (Blue)	Complete the game.
Old Armor B (Brown)	Complete the game.
Rider	Complete Chapter 6 with an "A" or better rank.
Special	Collect all Ishtar Bone Fragments from the Dark World portals. Note: When wearing this costume you will not take damage, but will not get points for fighting or collecting items.