Pursued by monsters along walls and up and down ladders, your only hope of survival is to trap them in holes which you dig in their path. If a monster falls in, the hole must be filled in completely or the monster will crawl out.

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.

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.

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

If you score 3,000 you earn an extra life.