When you complete missions in the game with the indicated requirement the corresponding Bonus scenario will become unlocked.

Unock Beginnings 1 Scenario:
Complete Train Derailment 3.

Unock Beginnings 2 Scenario:
Complete Beginnings 1 with an 'A' or better rank.

Unock Fourth Survivor Scenario:
Complete all scenarios.

Unock Rebirth 1 Scenario:
Complete Mansion Incident 3.

Unock Rebirth 2 Scenario:
Complete Rebirth 1.

Unock Nightmare 1 Scenario:
Complete Mansion Incident 1.

Unock Nightmare 2 Scenario:
Complete Nightmare 1 with an 'A' or better rank.

Unock Death's Door Scenario:
Complete Racoon's Destruction 3 with an 'A' or better rank.

Unock Dark Legacy 1 Scenario:
Complete Fall Of Umbrella 3.

Unock Dark Legacy 2 Scenario:
Complete Death's Door and Nightmare 2.

Get an 'S' rank in ALL the scenarios so the message 'Unlimited Ammo Deactivated' appears on the screen. Ignore this message as it is a mistake as the word 'Deactivated' was used instead of 'Unlocked' and go to the 'Customise' menu and buy the Level 5 (Unlimited Ammunition) upgrade.

When you play Mercenary mode and get a 4 Star or higher rank in a map the following characters can be unlocked.

Unlock Ada Wong the Secret Agent:
Get a 4 Star rank in the Pueblo map.

Unlock Jack Krauser the Army Veteran:
Get a 4 Star rank in the Castle map.

Unlock Albert Wesker the Leader of Alpha Team:
Get a 4 Star rank in the Waterworld map.

Unlock Hunk the Operative for the Umbrella Corporation:
Get a 4 Star rank in the Island map.

This is a great way of getting weapons, all you have to do is go to the inventory screen and select the 'Stricker'. When you exit the inventory press the B button followed immediately after by the minus button and you will now be able to equip any weapon you want (except the Striker) and move and shoot twice as fast as normal. To deactivate this glitch just select the Stricker.

To get this hidden weapon you must first unlock 'Hunk's scenario - Fourth Survivor' and play through it until you reach the Police station. In the lobby of the Police station there is a secret room next to the front doors which will open if you shoot it. On the left side of the room on top of the desk is the handcannon.

On any difficulty setting complete 'The Fourth Survivor' sub-mission and an option when selecting characters that resembles two pistols and says 'begin play with 2 players' will appear on the right side of the screen. In this mode both players play as the same character and there are only two aiming reticles on the screen to play with.

These items are unlocked when you have earned an 'A' or 'S' rank on the indicated Chapter.

Unlock Death Mask:
Complete Rebirth 2 with 'S' rank.

Unlock Emblem/Gold Emblem:
Complete Nightmare 2 with 'S' rank.

Unlock Battery:
Complete Dark Legacy 2 with 'S' rank.

Unlock Medium Base:
Complete Dark Legacy 1 with 'S' rank.

Unlock Valve Handle:
Complete Beginning 1 with 'S' rank.

Unlock Microfilm A/B:
Complete Beginning 2 with 'S' rank.

Unlock Slide Cartridge:
Complete Rebirth 1 with 'S' rank.

Unlock Film A/B/C/D:
Complete Umbrella's End 1 with 'S' rank.

Unlock Book of Wisdom/Future Compass:
Complete Raccoon's Destruction 1 with 'S' rank.

Unlock Chronos Key:
Complete Raccoon's Destruction 3 with 'S' rank.

Unlock Hex Crank:
Complete Nightmare 1 with 'S' rank.

Unlock Briefcase:
Complete Train Derailment 1 with 'S' rank.

Unlock Eagle/Serpent/Jaguar Stone:
Complete Fourth Survivor with 'S' rank.

Unlock Fuel Canteen:
Complete Mansion Incident 3 with 'S' rank.

Unlock Ink Ribbon:
Complete Umbrella's End 3 with 'S' rank.

Unlock Lighter Fluid:
Complete Raccoon's Destruction 2 with 'S' rank.

Unlock S.T.A.R.S. Card (Brad's):
Complete Death's Door with 'S' rank.

Unlock Square Crank:
Complete Umbrella's End 2 with 'S' rank.

Unlock Sterilizing Agent:
Complete Train Derailment 3 with 'S' rank.

Unlock V-Jolt:
Complete Mansion Incident 2 with 'S' rank.

Unlock Relief of Discipline/Obedience/Unity:
Complete Train Derailment 2 with 'S' rank.

When you have completed ALL the scenarios including the bonus sub-scenarios the Special Stage mini-game will become an unlocked.