Unlock Hunters Files:
Unlock the different Hunter's Files by doing the following:
Player Character Files - Finish Arcade Mode (multiple times)
Enemy Files - Kill/meet enemies (any mode except Training Mode).
Boss Files - Kill Bosses in all modes, including Training Mode.
Item Files - Buy/earn each item in Special mode.
Miscellaneous Files - Finish all missions in Special mode and complete Training Mode.
Unlock Free Play:
To unlock Free Play for Arcade Mode, beat all the Training Missions.
Gameshark Codes:
(M) Must Be On = EC8383AC144828E4
Inf Health P1 = 4CE0B3581456E79E
Inf Health P2 = 4CE0B4A01456E79E
Inf Ammo P1 = 4CE0B3941456E79D
Inf Ammo P2 = 4CE0B4DC1456E79D
Inf Credits = 4CE0AEFC1456E79D
Tons o' Silver = 4CE0D13C1456B00C