One of the simplest of all game premises is that which defines the objective of Centipede: shoot everything. Your gun is positioned in a mushroom field with the sole purpose of wiping out everything the garden can throw at you. This includes the mushrooms, centipedes, spiders, fleas and poisonous scorpions.
Your main adversary is the centipede which moves across the screen. When the centipede comes into contact with either a mushroom or the playing area, it turns and moves down a row. When you shoot a segment of the centipede, the head section continues on its way, but the rear section splits off, turns and moves down a row and leaves a new mushroom behind. In this way there can very many small segments of centipede at different levels of the playing area moving in either direction.
You also have to deal with the constant threat of spiders which appear from the side of the screen and move across the lower section of the playing area, bouncing up and down trying to hit you. You have free movement within the bottom 12 rows of the screen and the spider moves either from left to right or right to left until it leaves the screen. It does not change direction.
At certain stages of the game, the fleas are activated. Fleas drop vertically from the top of the screen leaving fresh mushrooms behind them as they fall, which can be very inconvenient when you are trying to completely clear a column of mushrooms.
Later on a scorpion will appear which moves from left to right in the upper areas of the screen poisoning any mushrooms it comes into contact with. If a centipede segment hits a poisoned mushroom the centipede falls vertically to the bottom of the screen without turning. This is very hazardous as if you are immediately above the falling centipede it will kill you.
Mushroom: 1 point.
Spider: 300, 600 or 900 points. The lower down the screen the spider is when you shoot it, the higher the score.
Flea: 200 points.
Scorpion: 250 points.
Starting lives can be set to 2, 3, 4 or 5 (default is 3).
Extra life can be set to every 10,000, 12,000, 15,000 or 20,000 points (default is 12,000).
Game difficulty can be set to Easy or Hard (default is easy).
If you can build two central complete columns of mushrooms near the centre of the screen with a clear column or two between them, centipedes will continually fall down the central gap. You can then just wait there continually firing and racking up points.
Pick off spiders as soon as you can after they appear. Spiders bounce up and down, but will try to home in on your position. If a spider appears from the left, you can move past it to the right, and this spider will not bother you, as they do not turn back. You are then safe from spiders until the next one appears.
New fleas will appear and continue to fall as long as you keep killing them. If you miss a few you will get a respite from any more appearing.
If you shoot a centipede at the edge of the screen and continue firing, providing you are high enough up the screen (or close enough to the centipede) you will pick off every segment.
Fleas cannot appear when a complete centipede is on screen.
You can build a shield of mushrooms completey around yourself with some strategic centipede killing. Then you can sit inside this shield and repeatedly pick off spiders, safe in the knowledge that centipedes will not reach you.