Complete the game once on any difficulty to gain the Special Key to open the costume room where you can change you clothes after completing the game the required amount of times.
Jill's Sarah Connor costume: Complete the game once with Jill on any difficulty.
Jill's Resident Evil 3 costume: Clear the game twice with Jill on any difficulty.
Chris' The Mexican costume: Clear the game once with Chris on any difficulty to unlock his costume where he dresses up like Brad Pitt from the movie The Mexican. Rebecca also changes her costume to look like Julia Roberts from The Mexican.
Chris' CODE Veronica costume: Clear the game twice with Chris on any difficulty.
Source: Brady Games Resident Evil Strategy Guide
Grenade Launcher Glitch:
This is a step by step guide to getting this glitch to work. Follow these instructions or it will fail.
Requirements: You must have the grenade launcher and two types of ammo (e.g., Grenade Rounds, Incendiary Rounds)
1) Put all items in item box
2) Put Grenade Launcher in upper-left item slot
3) Put Incendiary Rounds in upper-right item slot
4) Close box
5) Open inventory
6) Equip Grenade Launcher
7) Open box
8) Select Incendiary Rounds from inventory
9) Press ''A'' twice
10) Move cursor to Incendiary Rounds inside box
11) Press ''A'' twice
The amount of Incendiary Rounds in the Grenade Launcher will now increase. The number value will be graphically glitched. Close the box and open inventory to fix that. I assume the value exceeds the possible amount, so the game automatically reduces the rounds to 240 to prevent data corruption. Enjoy.
This also works for other types of grenade ammo... But why you'd want anything other than Incendiary Rounds is beyond me.
NOTE: This code does not work in the PAL version of the game.
Invisible Enemy Mode:
To unlock this mode beat Real Survival mode once.
Message from director and unused costumes:
Beat Invisible Mode in 5:00:00 to open up a message from the director and a slide show of unused costume designs.
New costume for Jill,Difficulty Select and New Title Screen:
Complete the game with Jill once and save the game.A few things will change.
1-The main menu will have a different background.
2-If you select the option'Once Again(with your save data loaded)'you will be given a choice of difficulties to begin the next game with-Easy,Normal and Hard
3-You will receive a key that enables you a costume change(in this case Jill's costume)
Contributed By: Jacen Solo, Source: Self
One Dangerous Zombie Mode
Complete the game as both Chris and Jill one time to unlock the ''One Dangerous Zombie'' option. A special zombie will continue to follow you around during the first part of the game. Shooting this zombie will end the game, so you must avoid it during game play.
Added by: jedi87 , ID#251