The person who wrote the D.I.J. diary is Alfred Ashford's butler. You can find this out by reading the butler's letter found in Claire's section of Antarctica.
D.I.J.'s journal
You find D.I.J.'s journal in the slot machine in battle mode. Sometimes you have to play more than once to find it.
D.I.J.'s REAL identity
Read the D.I.J. journal carefully and you'll find that D.I.J. is really a mouse! Pay attention to when Claire Gets trapped by the shudder just before Alfred talks to her on the intercom. And, the mouse in the locker on the antarctic base? D.I.J. Is NOT the butler. Did you see a butler in the cargo plane? Nope.
First Person Mode
To attain the first person mode, beat the game in easy or normal mode.
Get the rocket launcher
To obtain the rocket launcher (NOT the linear launcher which is the weapon used at the end of the game) finish the game with a rank S. To acquire an S ranking, you CANNOT save and retry (basically you cannot die or reset the game at anytime) and you CANNOT use health canisters to heal yourself. You must also give the black man at the start of the game the antitoxin and you must save Steve quickly when he takes the golden guns in disc 1. Also you must finish the game within 5 hours.
Infinite ammunition ( demo )
Enter the item selection screen, then press Up, Up, Down, Down, Left, Right, R.
Infinite Shotgun Rounds
Enter the room with the 2 paintings of the British Captain and the Facility Model, then go down the ladder and go back up. When you come back up, the shotgun rounds will be behind the pedestal. Go out through the door and return back to the room. Go down the ladder, go back up the ladder and the shotgun rounds will re-appear. Do this as many times as you want.
Linear Launcher
Get an A ranking with the two Claires, Steve, Chris and Wesker in the Battle Game to unlock the Linear Launcher. Once you gain it, it will automatically appear in your inventory when you begin the Battle Game again
Reset Game
To reset, just push start, A, B, X and Y at the same time, and the game will reset.
Shoot the screen
This is a very obscure cheat I noticed recently. This is sort of like the Re2 cheat where you can shoot the camera. You have to be where you've had Chris and now have Claire again, a little before you meet the Steve-Monster. You go past the first tentacle then get to the second one. Line up so that you only see Claire's back and she is very near to the tentacle (but not within its reach). Take out the grenade launcher, arm the normal rounds and fire at the tentacle. If you do it right the tentacle's green blood should splatter on the camera. Once you move Claire it goes away.
Solution to the seven paintings puzzle
About five hours in on the first disc you'll find a room with seven paintings, each with a switch below it. In order to solve the puzzle you must press the switches below each painting in the correct order. Below is the order in which this must be done.
1. Painting of the Woman
2. Man with two babies
3. Man by himself
4. Man with plate
5. Man with book
6. Man with candle
7. Big painting
Unlock Albert Wesker
Complete the Battle Game with Chris Redfield.
Unlock Steve in Battle Game
Solve a puzzle in the main game. In the underground Save Room in Chris' walkthrough, complete the drawer puzzle in the corner. Grab the Gold Luger to unlock Mr. Burnside.
