UFO (16K Spectrum)
by Julian Wood
from Your Computer (December 1984), pages 135-137

Julian Wood and a maze game with a difference for the Spectrum.

UFO Is an original game for the 16K or 48K Spectrum. It is written entirely
in machine code and is therefore very fast. The general idea of the game is
as follows:

You, a poor undefended human have been sent against a lethal race of aliens
who follow you around the screen. The only way you can kill an alien is to
collide with an energy block  the stationary object on the screen  which
gives you enough power to kill one, and only one, alien. Once you have
killed an alien, if you go to the bottom of the screen without hitting
anything and then press the down key, the dead body of the alien will appear
at the bottom of the screen.

Once the time  shown as TI at the top of the screen  reaches zero, the
number of dead aliens at the bottom of the screen gives you a bonus added to
your score. With each screen only a certain maximum number of aliens will
appear, and once you have killed all these, another batch will appear.

After each screen the maximum number of aliens is incremented up to a
maximum of 10. The keys for moving the human are:
6 = left, 7 = right, 8 = up, 9 = down, 0 = halt of the game.

After playing UFO for a while you may find it too easy or hard. I have
therefore shown various locations - in figure 1 - which you can change to
suit your needs by Poking. The initial contents of the location are shown in
brackets. To change a value of a location, just load the code, Poke the
location and

    RAND USR 25807


Figure 1.
    Speed = 25922 (20).
    Time speed = 25915 (3).
    Lives = 25839 (3).
    Max. number of aliens = 25689 (10).

If you are still unconvinced of how essential sound is in games, then try
the following:

    POKE 24500, 201 : POKE 25114,201.

Hear the difference?

Furthermore, try Poking 24775, 201.