Infinite Serum Vials in Killer 8 Mode:
At the Press Start screen, press Down, R, Up, L, Y, B, X, A. You get 100 serum vials every time you begin the first level. Just keep re-entering the first level to get as much serum as you want.
Game Mode Unlockables:
|Beat the game on Normal or Hard||Killer8 Hard Mode + Young Harman playable character|
|Beat Killer8 Mode||Hopper7 Mode|
Thanks to Revolution reader restrained!