Bonus characters:
To get each characters bonus player enter these codes at the options screen:

Blizzaro:
Up, Down, L1, Circle, Circle, R1, R2, L1

Pyro:
Up, Down, Circle, Down, L2, Down, R1, L2

Rex:
L2, R2, R1, Up, Square, R2

Tox:
Circle, Up, Square, Circle, Square, R1, L1

Kostra:
Up, Up, Square, L2, R2, L2, R2, Down

Lunarr:
Down, Down, L1, Up, Square, R2

Small players:
Beat "Challenge" mode on the easy difficulty level to unlock a secret option to make people small.

More speed:
Beat "Challenge" mode on the medium difficulty level to unlock a secret option for more speed.

Medium difficulty:
At the option screen, press Up, Square, R1, L2, L2, Up or beat challenge mode on the easy difficulty setting.

Hard difficulty:
At the options screen, press L2, Down, L1, R1 or beat challenge mode on the medium difficulty setting.

Expert difficulty:
At the options screen, press Square, Down, L2, Down, Circle, L2 or Beat challenge mode on the hard difficulty setting.

Alternate character appearance:
At the character selection screen, hold L1 or R1 and select a character

Quick start:
When the word "Go" is spoken when your character is at the starting line, press X (with the default controller setting). If timed correctly, your start will be faster than normal.