To keep you in the festive spirit I think I have discovered a bug in Llamasoft's Matrix to delight many frustrated C64 users who can't get past the first dozen or so screens.
One evening while hindering my friend's play we discovered the bug. If the joystick is pushed left while holding down the fire button, the zone can be cleared by pressing the Commodore key.
It is therefore possible to reach the elusive 20th screen where everything is thrown at you. Camels, diagonal tracking droids, the lot.