Super Smash Bros. Melee Easter Eggs
New Background Music for Gallery Mode
Once you have unlocked the Music Test, choose a song you would like to hear in the Gallery mode by pressing A. Now exit by pressing B, and then go to Gallery mode. Now you can look at trophies while listening to your favourite SSB: Melee song;)
Capt. Olimar trophy
If you start up SSBM with a Pikmin save on your memory card you will get a free trophy.
Peach's Secret Turnips
When Peach uses her Turnip attack, there is a rare chance that she will pull a hidden item out of the ground. These items include the Beam Sword, Bob-Bomb, Mr. Saturn, and a very sick-looking Turnip that deals obscene amounts of damage and can deal instant death at rather low percentages.
Hints & FAQs provided courtesy of GameFAQs.