Everything you need to know - Guide for Super Smash Bros. Melee

The following are in the order you COULD get them...

Jigglypuff - Do anything that involves Classic or Adventure Mode, and do it without continuing

Dr. Mario - Beat Classic Mode without continuing or losing a life

Luigi - Get a two in the second's time.  A cutscene will appear leaving you to battle Luigi and Peach.  At the end of the credits, The Big L will 

challenge you

Mewtwo - Play for 20 hours, or for 700 V.S. matches (Use tournament mode for the 700)

Ganondorf - Beat Event 29

Young Link - Beat Classic Mode with ten characters

Pichu - Beat Event 37, or for 200 V.S. matches (Again, use tournament mode for the 200)

Marth - Play once with all the characters, or play 70 V.S. matches (You know the answer)

Roy - Play with Marth in Classic Mode without continuing

Falco - Beat the 100 man melee

Mr. Game and Watch - Beat Adventure or Classic mode with all 24 characters or play 1,000 V.S. matches (ug...)

I will now tell you about the secret stages

Kongo Jungle Stage - Beat the 15 minute Melee (Use Donkey Kong, Down-b)

Kirby's Dreamland Stage - Break the Targets!

Final Destination Stage - Beat Event 51 (Use Jigglypuff, Down-b)

Classic Yoshi's Island Stage - Get over 1,300 feet with Yoshi in the Home Run Contest

Brinstar Depths Stage - Fight over 50 multi-player, or com-player matches (TOURNAMENT!)

Mushroom Kingdom II Stage (Subcon) - You could actually get this stage any time, but earn the Birdo and Pidgit trophies

Fourside Stage (Earthbound) - Fight over 100 multi-player, or com-player matches (Gee, do you remember?)

Big Blue Stage - Fight over 150 multi-player, or com-player matches (Have a good one }")

Pokemon Floats Stage - 200, tournament, make it happen!

Battlefield Stage - Beat the game in All Star Mode

Flatzone Stage - Beat the game with Mr. Game in Classic Mode without losing, or using (you know what I mean), a life

These are some Hints and Tips on the Events 1-51, note it may take me a while to do this

Event 1 - Trouble King - Mario - Smash that ol' Bowser, hold A to charge up shots
Event 2 - Lord of the Jungle - Donkey Kong - Use B, hit him while he's in the air, repeat
Event 3 - Bombfest - Jigglypuff - Down-b, or B, charge it first, though.
Event 4 - Dinowrangling - Jigglypuff - Let it fall off a cliff, or use Down-b
Event 5 - Spare Change - To heck with this, get lucky
Event 6 - Kirbys on Pirade - Jigglypuff - You know the answer

That's All Folks, I hear the Call of the Wild, but I'll return, you mark my word!  Peace.