To get the next set of events, you need to unlock the following characters: Young Link (Completeing the game with 10 characters, 1 must be Link)
Falco (Completing 100 man Melee)
Luigi (On Mushroom Kingdom in Adventure, get a 2 in the seconds place, e.g. xx.x2.xx. Once you do this, you will verse Peach & Luigi instead of Mario, defeat them in under a minute.
Jigglypuff (I think) (Complete Adventure or Classic Mode)
Once you unlock these four characters, the next set of events will be open to you, to get Pichu, you need to beat event 37: Legendary Pokemon.
To get the last set of events after that (Excluding event 51), you need to all 25 Characters.
To get event 51, you need to complete every event match.
I'm gone - bye