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Gamecube - Killer 7 cheats

Killer 8: 100 Serum Vials:
At the press start screen, enter DOWN, R, UP, L, Y, B, X, A 

Unlock Killer 8 mode and Young Harman as playable character:
Finish the game in normal or hard mode.

Unlock Hopper 7 mode:
Finish the game in Killer 8 mode. 

Watch different ending:
Finish the Killer 8 mode.