Monsters can be killed in one of two ways: either by falling through holes which you dig and fill, or by being hit by monsters from above. If a monster is hit by a falling monster, both die. If you manage to kill all the monsters, you graduate to another screen.

The longer you survive, the more you can score as the monsters vary and become more devious. Whereas red monsters only need to fall through one level, green monsters must fall through two levels and white monsters must fall through three levels before they actually die. If they fall through more than the minimum number of levels, then your score will be even higher.

From the second screen onwards, any red or green monster that is allowed to crawl out of a hole, mutates into a green or white monster respectively.

Quite an exhausting business, so keep an eye on the oxygen level which drops during each screen and eventually runs out, whereupon you will die. You have three lives, however, and can earn another one by scoring 3,000 points.

Sounds can be turned on and off with S (Sound) and Q (Quiet). ESCAPE escapes from a game.

Game Controls
Z - Left, X - Right, : - Up, / - Down, D - Dig, F - Fill

Standard joystick movements apply. To dig, hold joystick in down position and press fire button. To fill, hold joystick in up position and press fire button.

Scoring

Monster                      Monster Falls Through
           One level  Two levels  Three levels  Four levels  Five levels
RED           100         200         300           400          800
GREEN          -          300         500           700         1,500
WHITE          -           -          700          1,000        2,000