Double health/speed in Vs. Mode:
At the title screen, press Down, Down, Up, Down, Left, Right, Down, Up, Up, Up,
Up, Right, Left, X.
Extra Vs. Mode characters:
At the character select screen, press L, L, Down, Down, Black, White, Black,
White, R, L, Black, R, R, White.
Big characters at world map:
At the title screen, press Left, X, Up, Y, Right, B,
Vs. Mode Elephant Pool Arena:
Win 20 team battles.
Vs. Mode Metal Age Arena:
Win 100 arena battles.
Thanks to Revolution readers chipperdan and eegloo!