difficulty/stock with Mr. Game & Watch.
by Ganondorf; defeat him and you can play as him from then on.
15-Minute Melee. I'd recommend using Donkey Kong and constantly use his Down + B move the entire time.
seconds meter (03:12:43 for example). You'll then view a scene where Luigi
comes and kicks Mario away so he can fight you with Peach. Defeat them both, then go on and complete Adventure Mode. You'll have to fight Luigi; defeat him and you can play as him.
14 regular characters (not ones you've unlocked). Marth will then challenge
you; beat him to gain him as a selectable character.
Alternatively, you can simply use every character as a human player in VS. Mode, and get a challenge from Marth that way.
Time total), or play 700 matches (without quitting) in that mode. After
either requirement is met, Mewtwo will challenge you; beat him and you can
play as Mewtwo!