First Beat Classic mode with Zelda and beat jiggly puff. then Beat Adventure Mode with any other one of the origanal charcters not ones you unlocked except mario do not use him. When doing adventure mode on the first level make sure to follow these steps so you can unlock luigi
Luigi - Play in Adventure mode as any character and finish the stage 1 with a number 2 in the "seconds" digit of the stage timer (third from the right). Defeat Luigi in less than 1:00:00. Complete the remaining stages in Adventure mode, then defeat Luigi again to unlock him.
then beat classic mode with mario to unlock Dr. Mario
Then go to 100 man melee and use donkey kong to make it easier and use his down b move kill them don't move from the center and if they don't come to you go to them then go back to the center. After 50 of them they start coming a lot faster so it get's easier and the time go's by quicker then. You will then be challenged by falco beat him to get him.
Beat classic mode with 7 more of the origanal characters and sometime during that you should cahllenged by young link. If not try the for your seventh guy make sure it is link. Or do an eigth guy and make sure it is link.
Beat classic mode with all orginal characters to get marth and if you have been listening you should have been using the origanals so there should not be much to do.
Beat classic with marth to unlock roy.
Then start doing the events till you eventually get ganondorf and pichu.
That is the fastest way to get most of the characters. Then just unlock mewtwo read the cheats section to find out how. Then beat classic with whatever character you have not beat it with yet and get Mr. Game and Watch. Congradulations you got everybody.
To bad I have not taken the long steps to get mewtwo.
Beat classic with Mr. Game and Watch to get all star mode. If that does not work then beat classic with the guy you got luigi with. If that does not work then something went wrong because to have Mr. Game and Watch means to have beaten story mode with everybody.