Characters:
Jigglypuff: Pass the Adventure Mode
Dr. Mario: Pass the Classic Mode with Mario
Luigi: In Adventure Mode, clear the Mushroom Kingdom with a time that has two in the ones digit for seconds(doesn't matter how many miliseconds there are) to battle Luigi in Mushroom Kingdom's fight. Then pass the Adventure Mode.
Falco: Pass the 100-Man Melee
Marth: Play with every character in Vs. Mode
Roy: Pass the Adventure Mode with Marth
Ganondorf: Complete the Triforce Gathering Special Event
Pichu: Complete the Legendary Pokémon Special Event

Courses:
Mushroom Kingdom 2: Get the Birdo trophy(you can get it in the Lottery or in the Adventure Mode's stages)
Brinstar Depths: Play 50, 100, 150, or 200 Vs. Mode matches
Yoshi's Island Past: Hit Sandbag over 1,350 feet in the Home Run Contest with Yoshi(Thanks to Fyre Ball, AKA Mr. Gahkoo)

Fyre Ball/Mr. Gahkoo's Secrets:
Mewtwo: Play 700 vs. matches or 20 hours of vs. mode.
Mr. G & W: Beat Classic mode with the 24 other characters.
Kongo Jungle Past: Beat the 15 minute melee. (Use DK's down+B) (Note from Golem: he probably means in the Multi-Man Melee)
Dream Land Past: Clear Target Test with every character.
Battlefield: Clear All-Star mode
Final Destination: Clear all 51 event matches.
Fourside: Play 100 vs. matches
Big Blue: Play 150 vs. matches
Poke-floats: Play 200 vs. matches.
Flat Zone: Clear Classic mode with Mr. G & W

I (Golem) have achieved these secrets while playing the whole game itself; a previous factor mixed in with what I have done may have set off a new area or character. If you find a new way to do something, or a new thing in general, contact me at webmaster@mbgold.zzn.com.

Submissions and rebuttals should be e-mailed to nintendofanssite@yahoo.com. Proper credit will be given, and please tell me if you don't want your e-mail revealed on the site.