100 Serum Vials in Killer 8 mode - At the "Press Start" screen for Killer 8 mode, press Down, R, Up, L, Y, B, X, A. If you entered the code correctly, you will hear the healing sound. You will get the vials when you start Target: Angel. Repeat the level over with the code enabled to get another 100 vials.
Alternate ending sequence - Successfully complete the game on the Killer 8 difficulty setting to view an alternate ending sequence.
Hopper 7 mode - Successfully complete the game on the Killer 8 difficulty setting to unlock the Hopper 7 difficulty setting.
Killer 8 mode - Successfully complete the game on the normal or hard difficulty setting to unlock the Killer 8 difficulty setting.
Play as Young Harman - Successfully complete the game on the normal or hard difficulty setting to unlock Young Harman.