Running Wild Codes -

Medium difficulty:
Press Up, Square, R1, L2(2), Up at the difficulty selection screen.

Hard difficulty:
Press L2, Down, L1, R1 at the difficulty selection screen.

Expert difficulty:
Press Square, Down, L2, Down, Circle, L2 at the difficulty selection screen. Alternatively, successfully complete challenge mode under the hard difficulty setting to unlock another difficulty level.

Play as Blizzaro:
Press Up, Down, L1, Circle(2), R1, R2, L1 at the secret options menu.

Play as Pyro:
Press Up, Down, Circle, Down, L2, Down, R1, L2 at the secret options menu.

Play as Rex:
Press L2, R2, R1, Up, Square, R2 at the secret options menu. Alternatively, use the Elephant to successfully complete challenge mode under the hard difficulty setting.

Play as Tox:
Press Circle, Up, Square, Circle, Square, R1, L1 at the secret options menu.

Play as Kostra:
Press Up(2), Square, L2, R2, L2, R2, Down at the secret options menu.

Play as Lunarr:
Press Down(2), L1, Up, Square, R2 at the secret options menu.

Small people:
Successfully complete challenge mode under the easy difficulty setting to unlock a bonus option to make the people smaller. Note: This also unlocks the Jungle level under the medium difficulty setting.

Faster game:
Successfully complete challenge mode under the medium difficulty setting to unlock a bonus option for more speed.

Alternate character appearance:
Hold L1 or R1 and select a character.

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