Space Taxi/Mystery screen

The Mystery Screen, the game's bonus level, is reached by completing either the standard or random 24-hour shift.

Riddle
The most important part is the message at the bottom, which hints at the existence of some well-hidden extra features in the game, and reads approximately as follows:

"Eat a PIe until a 'FIRE' glows; go Up until it stops; touch a Star and you'll see the hidden Secret Menu!"

Solving the riddle
This secret menu is accessed not from the Mystery Screen, but at the Instructions screen, and as such is available at any time before beginning a new game. Go to the Instructions screen: the riddle is referring to 'FIRE' in the "Press 'FIRE' to exit" message at the end of the instructions. Press the Pi key (usually once or twice) until 'FIRE' turns from black to dark gray. Net, press the up-arrow symbol repeatedly until it returns to black. Finally, press the * key.

Secret menu
The secret menu is recognized by its red background and yellow border. Several options are available here, the most significant being:
 * Record a demo. Choose one of the four levels used by the game as demos, play the level and your gameplay will be recorded and replace the existing one.
 * Disable/enable sprite collisions. Items implemented with hardware sprites (projectiles and things floating around) won't impact the taxi.