Sound test
At the title screen, press Left + A + C-Left + C-Right + Start.

Bonus ending
Get an "A" on every level and collect the fifty-two gold gems. Then during the ending sequence, hit the target on Teren that appears for a slightly different version.

Bonus levels
Collect all fifty-two gold gems and view the entire ending sequence. Press R after the last screen with the stages appears to access twelve bonus levels.

Skip introduction sequences
Press Z.

Faster speed
Repeatedly tap Right during any of the running sequences to move faster and win the race.