Unicycle!

Level select:
Hold [Ctrl] while selecting the new game option. A dialog window will appear, allowing any level to be selected. Note: Codes cannot be used in multi-player mode.

Invincibility:
Enable the "Level select" code, then enter Supercycle! as a level. Alternately, hold [Cmd] + [Ctrl] during game play.

99 lives:
Enable the "Level select" code, then enter Computer error in your favor as a level.

Destroy wall:
Type wall during game play.

Avoid falling in pits:
Enable the "Level select" code, then enter Flying man as a level.

Bonus level:
Enable the "Level select" code, then enter BONUS as a level.

No pits:
Enable the "Level select" code, then enter Ditch be gone as a level.

No walls:
Enable the "Level select" code, then enter Away, ye scurvy walls! as a level.

Psychedelic colors:
Enable the "Level select" code, then enter psycho! as a level.

Sound test:
Enable the "Level select" code, then enter music as a level.

Double points:
Enable the "Level select" code, then enter CHEATER! as a level.

Double happy face points:
Enable the "Level select" code, then enter CHEATER? as a level.

Level 0:
Enable the "Level select" code, then enter 0 as a level.

Smart wall land:
Type smashed at the main menu.