Double health/speed in Vs. Mode:
At the title screen, press Down, Down, Up, Down,
Right, Down, Up, Up, Up, Up, Right, Left,
Extra Vs. Mode characters:
At the character select screen, press L1, L1, Down, Down, R2, Select,
R2, Select, R1, L1, R2, R1, R1, Select.
Big characters at world map:
At the title screen, press Left, , Up, ,
Right, , Down, .
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!