To Get Captain Falcon you must beat the one player mode in under 20 minutes. I suggest doing it on very easy mode so it is eaisier to get him.

#2 Jigglypuff

For Jigglypuff all you have to do is beat the game in any mode.

#3 Luigi

Luigi is activated when you complete the bonus one stage with the original eight characters. You can play the bonus one practice with the eight to get the same effect.

#4 Ness

To enable Ness you must beat the game in Normal mode with three lives without continuing. This is very hard and he will most likely be the last character you will get.