You are currently in Melee Mode.
Here is how you get the 11 hidden characters.
Beat a one player game (Classic or Adventure Mode) and Jigglypuff will challenge you. Win and you will be able to play as her.
Chosse Adventure mode with any character. On the first level, go across the finish line when the time is at 2 seconds (Example: 5:02,2:02,ect) You will see a clip of Luigi jumping on mario. Now you will have to fight Luigi and Peach, don't lose a life and win in under 45 seconds. Now beat the rest of the game and Luigi will challenge you.
Beat Classic Mode with Mario on any level without continuing then beat Adventure Mode with Mario without losing a life.
Complete classic mode with 10 characters, 2 of the characters must be Zelda and Link.
The easiest way to get marth is to play vs. mode with all 14 default characters, computer players don't count. You can also get Marth by beating classic mode with all 14 default characters.
After you get marth, beat classic mode with marth without losing a life, or beat adventure mode with any character without continuing.
Complete event # 29.
Complete the 100 MultiMan Melee.
Complete event # 37.
Mewtwo takes a long time to get. You have to play vs. mode for 20 HOURS. The computer doesn't count. To see your time, on the main menu, go to Data, Melee Records, Misc. Records. Look at combined vs. play time. If you play with more than one human player, your time go up faster (Example: if you play for 5 hours with 4 human players, it would equal 20 hours)
Mr. Game and Watch:
Complete Classic or Adventure mode with 24 characters.