Simply complete the game once in order to unlock this additional mode. FYI: Even though you are not prompted to save after the game's end credits roll and you are notified that the Battle Game mode has been unlocked, you needn't worry; the game will automatically create a separate save file that will mean that even if you accidentally overwrite your original save file with a new one, you will still be able to access the Battle Game mode.
First-person View in Battle Game
Just complete the main game. It has long since been argued that the only way to unlock first-person view mode in Battle Game was to successfully snipe the Nosferatu boss in the hear with Alfred Ashford's Remington M700 sniper rifle, followed by completing the game, but this has since been debunked.
Play as 'Alternate Claire' in Battle Game
Complete the Battle Game mode once with Claire Redfield to unlock her alternative outfit and weapon loadout.
Play as Steve in Battle Game
During your playthrough of the main campaign, make sure to collect the single gold Luger replica that is locked inside the cabinet in the basement office save room, shortly after the part where you pass a tank and descend a ladder as Chris Redfield. The correct open sequence for the drawers is: Red, green, blue, and brown. Make sure that the Luger is stored in the item chest for the remainder of the game, as it bares no other uses than to unlock Steve in Battle Mode upon completion of the game.
Play as Wesker in Battle Game
Complete the Battle Game mode once with Chris Redfield to unlock Wesker.
Infinite Ammo Rocket Launcher
This monster of a weapon will be awarded to you on a followup playthrough after completing the game with an A-rank. It'll be waiting for you in the first item chest that you come to. In order to score an A-rank upon completion, you must fulfill the following criteria:
- Complete the entire game in less than 4 hours, 30 minutes.
- Complete the game without using a single ink ribbon to save (disc-swap and those periodic game-prompted save options appear to be accepted).
- Promptly save Steve when he is trapped in the projector/luger room.
- Give Rodrigo the Hemostatic Medicine and Lighter.
- Attempt to rescue Rodrigo as quickly as possible from the Gulp Worm and collect the Lighter.
- Complete the game without using any First Aid Sprays.
- Complete the game without dying and using the 'Retry' option.
Avoid invading zombies in security hall
Alloy TG thingy, use security thing lol
Keep the Empty Fire Extinguisher!
Only way to get Magnum lol
Kill zombies in 1 hit on way to Palace / Military Training Facility
Knock over railing
Ward off bats with the Lighter
they dun like it lol
Get Lockpick as Claire
Give Rodrigo the Hemostatic Medicine. Lose Lighter
Regain Lighter as Chris
Save Rodrigo quickly during worm boss. Four explosive bow gun arrows will do the trick.
Locked 'n' Loaded Chris
Before Nosferatu boss fight, remove all weapons and items except the Gas Mask and Oct. Valve.
Easy Adult Albinoid Battle
Don't fight 'im. Simple as that. Dive into the pool (preferably with your health in the green), nab that Eagle Plate, dart out again and Bob's your uncle. Not a single shell of ammo expended, and the Adult Albinoid can merrily carry on practicing the back stroke. Everybody's a winner. Of course, you'll take a little damage for your little wet jaunt, but nothing a green herb couldn't remedy.