To unlock Masters Of Knifing mini-game, successfully complete the game.
To play the following characters in Multiplayer mode, do the following:
Albert Wesker: get a "B" or greater rank in the Masters Of Knifing mini-game
Barry Burton: complete Rebirth mode with Jill
Enrico Marini: complete all Co-Op levels in Multiplayer mode
Forest Speyer: complete Classic mode with Jill
Kenneth J. Sullivan: complete Classic mode with Chris
Rebecca Chambers: complete Rebirth mode with Chris
Play as Richard Aiken: complete all Versus mode levels in Multiplayer mode