Killer7

Killer 8: 100 Serum Vials:
Press Down, R1, Up, L1, Square, Triangle, Circle(2), at the the "Press Start" screen. The healing sound will confirm correct code entry. You will get the vials when you start Target 00. Repeat the level over with the code enabled to get another 100 vials.
pinhead via Anthony Skatz.

Killer 8 mode:
Successfully complete the game under the normal or hard difficulty setting. Young Harman is a playable character in this mode.

Hopper 7 mode:
Successfully complete the game in Killer 8 mode.

Alternate ending sequence:
Successfully complete Killer 8 mode.
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Hint: Faster blood vials:
When you have lots of "thick blood" and you do not want your machine to stop working with two or three conversions, tap Start + X repeatedly when the blood is converting. Do this as fast as possible and you will see the vials being produced faster than normal and with less blood.
Isaac Cortes Lara.

Hint: Climbing stairs faster:
When your character is going up on a set of stairs and slows down, do the following trick. Turn your back to the stairs and start running, then do a quick turn as soon as you start running. You will climb the stairs faster.
Isaac Cortes Lara.