Double health/speed in Vs. Mode:
While you are at the title screen press Down, Down, Up, Down, Left, Right, Down, Up, Up, Up, Up, Right, Left, X.

Extra Vs. Mode characters:
While you are at the title screen press L, L, Down, Down, Black, White, Black, White, R, L, Black, R, R, White.

Big characters at world map:
While you are at the title screen press press Left, X, Up, Y, Right, B, Down, B.

Vs. Mode Elephant Pool Arena:
Win in 20 team battles.

Vs. Mode Metal Age Arena:
Win in 100 arena battles.