100 Serum Vials in Killer 8 mode
At the "Press Start" screen for Killer 8 mode, press Down, R1, Up, L1, Square, X, Triangle, Triangle. 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.
Thick Blood and Serum
Thick blood is not carried over from stage to stage, but serum is. The blood machine in each stage will cease to function if you revisit the stage, so learn to collect as much thick blood as possible in a stage and break the machine before moving on.