You can get up to 33 characters for the multi-player mode. All you
have to do is beat the game on agent mode.
Extra Multi-Player Stages
Beat the second Severnaya bunker, water cavern and military archive stages in agent mode and they will then be accessable for multiplayer play.
007 Mode
After beating every single level in the game on the "00 Agent" difficulty setting, including bonus levels 19 and 20, a special "007 mode" opens up. This is a level editor level.
Players can configure options such as reaction time, accuracy, enemy health, and more cool stuff.
This code came from Ken Lobb of Nintendo himself!