Dr. Mario:
Successfully complete the game in classic mode as Mario without losing a life.

Alternately, play 100 versus mode matches. The winner of the 100th match will fight Dr. Mario. Defeat him and he will become a playable character.

Instead of shooting fireballs like Mario, Dr. Mario shoots pills that make your opponent change color. Dr. Mario's cape is just the coat on his doctor uniform.

Falco Lombardi:
Complete the 100 man melee.

Gannondorf:
Complete event mode #29 to unlock Ganondorf.

Jigglypuff (Purin):
Successfully complete the game with any character under any difficulty setting. Continues are allowed.

Luigi:
Complete the first stage of adventure mode with a time of xx:x2:xx. You will have to battle Luigi and defeat him in under one minute. Finish the remainder of adventure mode. At the end of adventure mode you will fight Luigi. Defeat Luigi and he will become a playable character.

Alternately, Play adventure mode as the Princess. At Princess Peach's castle, Luigi will take Mario's place in the opening intermission. Win this board. Proceed to win adventure mode with Zelda. Luigi will attack again after the credits complete. Defeat him again to unlock him. Lives, continues, and difficulty settings do not matter.

Mewtwo:
Mewtwo will appear at random at the end of a multi-player match and challenge the winner. He will be unlocked as a selectable character after he is defeated. Alternately, in versus mode, play 700 battles or get a total of 20 hours of game play.

To get Mewtwo easily, go into Custom Rules Melee and change "Stock" to "3" and "Item Flow" to "None", and "Stock Time Limit" to "Off". Choose two of your best characters (for fighting Mewtwo) and go into a match in the Pokemon Stadium level. Place both fighters on the Pokeball in the middle. Do not pause the game. Unplug the controllers, and leave the system on overnight to accumulate game time. Plug in the controllers again, and have one of the fighters die three times. If enough hours have been obtained, Mewtwo will challenge you. Defeat him to unlock him next to Jigglypuff as a playable character.

Mr. Game & Watch:
Complete the game in classic mode with all other 24 characters or complete target test mode with all other 24 characters.

Alternately, complete the game in classic mode with all 14 default characters under any difficulty setting, in any stock number, without using continues.

Pichu:
Accomplish one of the following:

Unlock both Luigi and Falco to unlock event #37. Complete event mode #37. After winning, Pichu will become playable.
Complete adventure mode as Mewtwo.
Play 200 matches in versus mode.
Prince Marth:
Either play 70 rounds in versus mode or play with all 14 default characters in versus mode.

Roy:
Successfully complete the game as Prince Marth in classic mode.

Young Link:
Finish classic mode 10 times. One time must be with Link, and another time must be with Zelda.

Alternately, complete adventure mode as Ganondorf.

Battlefield stage:
Successfully complete the game in All-Star mode.

Big Blue stage:
Fight over 150 multi-player matches.

Brinstar Depths stage:
Fight over 50 multi-player matches.

Congo Jungle stage:
Successfully complete the game in 15 Minute Spar mode.

Dream Land stage:
Successfully complete the game in Break The Targets mode with all fighters.

Final Destination stage:
Successfully complete event mode #51.

Flatzone stage:
Successfully complete the game as Mr. Game & Watch in classic mode without losing a life.

Fourside stage:
Fight over 100 multi-player matches.

Inside an NES Stage:
Unlock Mr. Game & Watch, then successfully complete his event.

Pokemon Floats stage:
Fight over 200 multi-player matches.

Yoshi's Island stage:
Hit over 1200m in home-run derby mode.

Extra Events (#31-#39):
Complete the first 30 events and unlock Jigglypuff, Luigi, Dr. Mario, Falco, and Young Link

Extra Events (#40-#50):
Unlock all characters and stages.

Event #51:
Clear all other events.

Alternate music:
Hold L or R and select a stage in multi-player mode. Keep the button held until the match begins. Note: Only certain stages have new music.

Sound test:
Successfully complete all 51 Events.

All-Star mode:
Unlock all bonus fighters to unlock the single player All-Star mode. This mode allows you to fight all game characters, but with less health items.

Star Fox mini-game:
Finish a one player game in classic or adventure mode. You will then enter a Star Fox-like mini game with names as targets. Shoot them to see more information about them. At the end, you will see how many hits you made. Hits made while the screen is stopped do not count.

Pikmin trophy:
Insert a memory card with a saved game from Pikmin. Begin the game and a Pikmin trophy will be available.

Wave Race: Blue Storm trophy:
Insert a memory card with a saved game from Wave Race: Blue Storm. Begin the game and a Wave Race: Blue Storm trophy will be available.

Alternate trophy background:
Zoom in on a trophy, then press Start to change the background.

Glitch: Misspelling:
Play the Stamina Melee as Roy and have Mario as an opponent in Pokemon Stadium. Pause game play and focus on the score board in the background. It will display Mario's name as "Nario".

Unlock Score Display
To unlock the Score Display for VS. Mode, play a combined VS. time of 24 hours. Score Display shows the current score for each combatant. Activate Score Display by going to Additional Rules in the Custom Rules screen

Hint:

Nintendo game systems:
Go to the trophy section to see most of the Nintendo game systems. Go to collection and zoom in on the background to the right of the television.

Completing event mode #13:
To easily complete event mode #13, pick up the egg and repeatedly jump back and forth over the stage.

Completing 15 Minute Melee:
Start the game as Donkey Kong. Position yourself under the platform on the left or right side of the screen and begin doing his Down + B move to slap the ground. Do this as long as you can. Watch out for bombs, Pokemon, or any other hazards that might break through this great move.

Completing 100 Man Melee:
Play as Donkey Kong. Stay in the center of the stage, and repeatedly do his Down + B move. After defeating all of the wire opponents, you will face Falco. Defeat him and he will become a playable character.

Hint: Raising multi-player match count:
To easily obtain the amount of multi-player match counts needed to unlock Mewtwo and several levels, set the custom rules on a stock game to one life, pause off, and random selection of stages. Start a super sudden death match, choosing a relatively fast opponent set at CPU level 9. Start the match and press Start continuously as needed, allowing the CPU to defeat you until your match count raises to the desired amount.