On the main menu hold L1 + R1 and input DOWN, CIRCLE, UP, SQUARE, DOWN, DOWN, UP, UP. When the shoulder keys are released, an extra cheat menu will appear.

While playing, input the following codes via the cheat menu for the following effects:

KK BigBlast - Equip shotgun
8wonder - Invulnerability (damage visual still present).
GrosBras - One-hit deaths on.
KK 999 mun - Adds 999 rounds to current weapon magazine.
lance 1nf - Press reload to summon lance.
KKcapone - Current weapon becomes submachinegun.
KKtigun - Current weapon becomes handgun.
KKsn1per - Current weapon becomes bolt action rifle.

Input the following codes on the main menu for higher game functions:

KKst0ry - Unlock all chapters.
KKmuseum - Unlocks all extras.