Here is a list of all of the unlockables in Super Smash Bros. Melee and how to unlock them.

Characters

Jigglypuff - Clear Classic or Adventure mode with any character or play VS. Mode 50 or more times

Luigi - Cross the finish line in Mushroom Kingdom in Adventure Mode with a 2 in the seconds and then complete Adventure Mode or play VS. Mode 800 or more times

Young Link - Clear Classic or Adventure Mode with 10 or more characters, two of them must be Link and Zelda/Sheik or play VS. Mode 500 times

Dr. Mario - Clear Classic or Adventure Mode with Mario without using any continues or play 100 VS. matches

Ganondorf - Clear Event Match 29 or play VS. Mode 600 times

Pichu - Clear Event Match 37, Clear Classic Mode with Mewtwo, or plat VS. Mode 200 times

Marth - Use the 14 original characters at least once in VS. Mode or play 400 or more VS. matches

Roy - Clear Classic Mode with Marth without using a continue or play 900 or more VS. matches

Falco - Clear the 100 Man Melee or play VS. Mode 300 or more times

Mewtwo - Play 20 hours combined in VS. Mode or play VS. Mode 700 times

Mr. Game and Watch - Clear Target
Test, Classic, or Adventure mode with all 24 characters or play more than
1,000 VS. matches

Stages

Planet Zebes: Brinstar Depths - Play 50 or more VS. matches

Eagleland: Fourside - Play 100 or more VS. matches

F-Zero Grand Prix: Big Blue - Play 150 or more VS. matches

Kanto Skies: Pokefloats - Play 200 or more VS. matches

Mushroom Kingdom II - Get the Birdo or Pidgit Trophy from Super Mario Bros. 2

Superflat World: Flat Zone - Defeat Classic Mode with Mr. Game and Watch

Battlefield - Clear All-Star Mode with any character

Final Destination - Clear all 51 Event Matches

Dream Land (N64 Classic) - Clear Target Test with all 25 characters

Yoshi's Island (N64 Classic) - Hit the Sandbag 1,323 feet or more with Yoshi on Homerun Contest

Kongo Jungle (N64 Classic) - Clear 15 Minute Melee with any character

Game Modes

Event Matches 31-39 - Clear the first 30 Event Matches and unlock Jigglypuff, Luigi, Dr. Mario, Falco, and Young link

Event Matches 40-50 - Unlock all characters and stages

Event Match 51 - Clear all previous events

Sound Test - Unlock every stage and character

All-Star Mode - Unlock all characters

Other Things

Fight Big Kirby - If you beat the Kirby team in less than a minute, you will fight a giant Kirby.

Cheats, Tricks, and Glitches

Start Match as Sheik - Keep on holding down the A
button when you pick Zelda on the character select screen. When the
battle begins, you will hear the "unlock chime" from Legend of Zelda and
you will start out as Sheik.

Play as Master Hand - "Make
sure the controller that will play as Master Hand in the 3rd controller
port. A second controller should be in the first or second port. When
you are on the Character Select screen in regular VS. mode, select any
character with the 1st/2nd port controller. Make sure the controller in
port 3 doesn't select or touch any characters at the selection screen.
Direct the 3rd controller down to "Name Entry", and the 1st/2nd
controller to "Back" at the top right of the screen. Have both
controllers press "A" at precisely the same time, which will bring you
to the Stage Select screen. If you do this wrong, you will go to a
different screen, so start over. If you end up at the Stage Select
screen, start a game and Master Hand will be a playable character."- IGN Here are a list of his moves: D-UP + B = Laser beams
D-RIGHT + B = Gun
D-UP + A = Rocket Ship
D-RIGHT + A = Shieldbreaker Punch
D-DOWN + A = Smack
D-RIGHT/UP + Z = Grab
D-UP + R = Drill
D-LEFT + R = Poke
D-RIGHT + R = Charged Punch
D-DOWN + R = Charged Slap
D-UP + L = Swat Away
D-DOWN + L = Finger Walk
D-RIGHT + L = Cross-stage Slap. Once the game ends, it will either crash or say that your character is Sheik.

I hope this was helpful.

tgags123 : Nice job on this! I like how you were short and sweet so that I didn't have to read a bunch of extra nonsense! Great job!

Barathemos : Thank you I appreciate it.