Playing as Ada and Chris Redfield
Finish both scenarios with rank A. You will receive powerful weapon, the 'Hunk' Mission, and another one called 'Ex-Battle' that wasn't available on the PSX version.
In 'Ex-Battle' Mission, you can play as Leon, Claire, Ada, and a bonus character from the first Resident Evil - Chris Redfield. Each character will have their own arsenal. The Mission is to find 4 anti-BOW bombs in the Police station. The characters will start from the lab and must backtrack to the station to find it. There also a time record for the fastest player.
Alternatively, you can play these special Mission, including 'Tofu' by accessing Windows 9x's registry editor. Search for HKEY_LOCAL_MACHINE\SOFTWARE\CAPCOM\RESIDENT EVIL2\ and enter the value '8'.