Super Smash Bros.
Fighter's Stance Trick
As you know when you tap the L button your character does his "fighters stance". If you go up to an enemy as Luigi and tap the L button he'll swing his foot, if your close enough he will kick him. It's not very effective but it's kinda cool.

Japaneese Version:Item Menu
Go to Vs. Mode, pick any 3 computer players and your favorite character to play. Play the "stock" mode, and set the lives to 10. Change the computer handicaps to 5. Play, if you are the victor, to you go the spoils! Enter options under vs., then go to items switch. You can choose what items will show up and how often they do. Bob-ombs galore! Infinite hammers!
Credit Goes To: via N64cc

 Fighter's Stance Trick
 Item Menu(Jap)
 Instant Death(Bat)
 Crowd's Favorite
 Additions To Opening
 Pokemon in Pokeball
 Kirby's Power Loss
 Borrow A Life
 Item Menu(US)
 Sound Menu
 Mushroom Kingdom
 Secret Characters
 Change Outfits
Instant Death By Homerun Bat
If you have a homerun bat, you can instantly knock off the enemy! Once you have the bat, tap forward and press A. If you're character blinks, you did it right. If you connect with this swing, the enemy will be blown away and instantly defeated!

Crowd's Favorite
You can get the crowd to cheer for your character! If you're hit percent is over 100, and start knocking people off without getting hit, you'll get the crowd to cheer for your character!
Credit Goes To: SMASHBrother( via N64cc

Added Character's to the Opening
After you unlock a secret character that character will no longer be a shadow in the opening sequence of the game!
Credit Goes To: Jason Krieger via N64cc

Pokémon in the Pokéballs
The Pokemon in the Pokeballs have the following powers:
Beedrill - Flies off to get the rest of its hive to attack the opponent.
Blastoise - Blasts opponent with water spray.
Chansey - Pops out and give you an item.
Charizard - Starts to breath fire in each direction.
Charmander - Just blows fire in one direction (only in Silphco stage).
Clefable - Arrives and mimics one of the other available Pokemon's attacks.
Goldeen - Flops around trying to hurt opponent.
Hitmonlee - Comes out and flies at the opponent doing a kick attack.
Koffing - Arrives and starts blasting foul smoke in the air.
Meowth - Pops out and showers out coins that hurt opponent.
Mew - The special secret 151st Pokemon makes his appearance and flies away.
Onix - Shows up, flies up top, and then boulders drop from the ceiling.
Porygon - Rams you or the opponent (only in Silphco stage).
Snorlax - Pops out, flies up, and then comes down huge, hurting your opponent.
Starmie - Finds opponent and blasts them with rays.
Venusaur - Razor Leaf attack; leaves from this Pokemon fly at opponents (only in Silphco stage).
Credit Goes To: oNe via N64cc

Kirby's Power Loss
Everybody knows that Kirby can swallow his opponents and take on some of their powers in this game, but what if you accidentally "ate" a character you didn't want -- and you want to pursue someone else? Simple: Just press the L Button to pull off Kirby's "Hello!" taunt and he will discard whatever power he took on.
Credit Goes To: Cranky's Island via GameSages

Borrow A Life
When playing a team multiplayer match, if you are defeated, but your team mate still has 1 or more life in stock. You can use one of his life to get back in the action by pressing A+B+Z+Start. Be sure to ask for permission from your friend.
Credit Goes To:CSHsia via IGN 64

Item Menu
Play the Versus Mode custom menu 50 times and an item menu will become unlocked that enables you to set all the multiplayer options you would wish for. You can determine which items will show up in the battles, and which won't. You can now have all-lightsaber battles or shower players with Pokeballs.
Credit Goes To: / Team IGN via IGN 64

Sound Menu
Beat Bonus Stages one and two with all 12 characters. You need to have unlocked the four secret characters first. Now go into the Data section.

Classic Mushroom Kingdom
To access the hidden classic Mario stage (complete with POW signs, Piranha plants, warp tubes and elevator), beat the game's one-player mode with each character and battle in each of the 8 stages. At the end, the game will tell you that you can now access Classic Mushroom Kingdom in the versus mode.

Secret Characters
Captain Falcon - To unlock Captain Falcon, beat the 1P Mode in under 20 minutes. Beat him in battle and he's yours.

Luigi - To play as Luigi, pass the Bonus Practice 1 with at least 8 main characters. When Luigi challenges you, defeat him and he's yours.

Ness - To play as ness, beat the one-player mode with any character with 3 lives, on normal difficulty. You must beat the game without continuing.

Jigglypuff - To play as Jigglypuff, beat the game within 20 minutes.

Change Outfits
You can change your characters' outfits by tapping the four C Buttons at the character select screen. Some costume changes are limited to colors, but characters like Pikachu are also available with hat.
Credit goes To: N64cc