Infinite ammo:
During play, go to the Inventory screen and press Up, Up, Down, Down, Left, Right,
Left, Right, Aim. 

Hard Mode:
Beat the game to unlock a more difficult game mode. 

Special Missions:
You can play special Missions, including Tofu's adventure by accessing Windows
9x's registry editor. 
At first you have to make a backup from your REGISTRY! In this part:

[HKEY_LOCAL_MACHINE\Software\CAPCOM\RESIDENT EVIL2] you have
to make a change: value 8. so it now reads

HKEY_LOCAL_MACHINE\Software\CAPCOM\RESIDENT EVIL2\
VALUE 8

It will release all of the extended players : Tofu,Hunk,EX battle .