Super Smash Bros. (N64)

Change outfits
Each fighter has four different color schemes. On the character select screen, press any of the C Buttons to change a fighter's colors. Pressing C-Up will show the default outfit.
Camera swivel
When viewing a character profile screen, hold Z and move the Control Stick around to swivel the camera around the character.
Bad buddy
If you lose all your lives during a Vs. mode team battle, press Start to use one of your teammate's stock lives and get back in the fight. This will work as long as your teammate has at least two lives left.
Unlock Jigglypuff
Beat the 1-Player mode at any difficulty, with any amount of stock lives, and you will fight Jigglypuff. Defeat him and he will be available on the character select screen.
Unlock Luigi
Complete Bonus 1 Practice mode with all eight standard (non-hidden) characters and you will fight Luigi. Defeat him and he will be available on the character select screen.
Unlock Ness
Beat the 1-Player mode on at least the normal difficulty, with three stock lives, without continuing, and you will fight Ness. Defeat him and he will be available on the character select screen.
Unlock Captain Falcon
Beat the 1-Player mode under 20 minutes and you will fight Captain Falcon. Defeat him and he will be available on the character select screen.
Unlock the Mushroom Kingdom stage
Beat the 1-Player mode with all eight standard (non-hidden) characters, and play in all eight battle arenas in Vs. mode to enable the classic Mushroom Kingdom arena.
Unlock the Item Switch
Play 100 matches in the Vs. mode. Item Switch gives you complete control of the items that appear in the Vs. mode battles.
Unlock the Sound Test
Complete Bonus 1 Practice and Bonus 2 Practice modes with all 12 characters.