Resident Evil 4 Cheats:

Extra Costumes:

Complete the main game to unlock new costumes for Leon Kennedy, Ashley Graham and Ada Wong. Additional costumes can also be unlocked by completing Separate Ways.

Professional Mode:

Complete the game and you can then select this difficulty setting when starting a new game.

Separate Ways:

Complete the game to select this additional mode from the main menu. Separate Ways allows you to experience events in the shoes of the mysterious Ada Wong. Gameplay comprises of areas from the Village, Castle and Island.

Ada's Report:

Complete each chapter of Separate Ways to obtain a section of Ada's report under the 'Extras' menu -- finish the whole of the game to unlock all five entries.

The Mercenaries:

Complete the game to unlock this additional mode. The Mercenaries allows you to control a number of characters from the Resident Evil universe over four different locations, in an attempt to rack up the highest score possible.

To unlock each secret character, meet the following requirements:

Ada Wong: Obtain a four star ranking on the village map
Jack Krauser: Obtain a four star ranking on the castle map
Hunk: Obtain a four star ranking on the Island map
Albert Wesker: Obtain a four star ranking on the Waterworld map

PRL 412:

Complete the game on the ‘Professional’ difficulty setting to unlock this PS2-exclusive weapon. The PRL 412 can be tweaked to function in one of two ways; stun or kill, and has unlimited ammunition.

Matilda:

Complete the game to unlock this special weapon. The Matilda is based off of Kennedy’s H&K VP70 upgraded handgun from Resident Evil 2, and fires three shoots in rapid burst.

Free Punisher Handgun:

Shoot ten or more of the blue medallions and visit The Merchant to acquire this weapon for free. The Punisher is a fast-firing 9mm handgun capable of piercing multiple targets in a row. Medallions are located in the farmyard and church sections of the village map.

Handcannon:

Obtain a five star ranking on all stages in The Mercenaries. You can then purchase this weapon from The Merchant thereafter using a new game plus file.

Chicago Typewriter:

Complete both the main game and Separate Ways; you can then purchase this weapon from the Merchant on a new game plus. The Chicago Typewriter is modelled after the infamous Thompson machine gun and uses infinite ammo, firing bullets that carry a damage ratio of 10.0 per shot.