I've heard that you can play with Master Hand by exploiting a glitch in Melee, what do I need to do to play as it?
I guess you are just asking this because you read on Kotaku: http://kotaku.com/5577690/the-super-smash-bros-secret-that-took-7-years-to-unlock
Anyway, here is your answer: http://super-smash-bros.wikia.com/wiki/Name_Entry_glitch
It can also be done with an Action Replay (gamecube only). This also lets you play as Giga Bowser!