Space Invaders/Walkthrough

Controls

 * Left/Right buttons: Use to direct the cannon along the bottom of the screen. Push left to move the ship to the left, and right to move the ship to the right.  Your cannon can not pass beyond the side of the screen.
 * Fire button: Press the fire button to send one missile directly above your position. You can only send one missile out at a time, but you have an unlimited supply of them.
 * 1 or 2 Players: Push these buttons to begin a one or two player game.

Cannon
You control the cannon. Use it to destroy the space invaders' formation. Direct the cannon left and right to choose a position to fire from. Time your shots so that they arrive at the location of an invader that you are trying to hit. Use the shields to protect the cannon from enemy fire. Be aware that both your fire and the enemy fire can chip away at the shields. Getting hit by an invader's bullet will result in the loss of one cannon. An extra cannon is typically awarded at 1500 points.

Invaders
The three alien invaders may look different, but they each behave the same. The remain in formation as they advance towards the surface of the moon. The entire formation will move to the right or to the left until the far column reaches the side of the screen. Then the formation moves down one row and returns to the opposite side of the screen. The lowest invader of each column will fire bullets down to the ground. If any one invader manages to touch down on the surface of the moon, the game is over.

Saucer
The saucer appears randomly over the formation. It appears on one side of the screen and crosses over to the opposite side. During this time, you can attempt to shoot it for bonus points. The point value that is awarded appears to be random, but it can be controlled to some extent by counting your shots (see below).

Scoring

 * Large Invader: 10 points
 * Medium Invader: 20 points
 * Small Invader: 30 points
 * Saucer: 50 ~ 300 points

Gameplay

 * Each stage begins with 5 rows of 11 aliens in formation.
 * Fire upwards between (or through) the shields to destroy the aliens. Destroy each alien to advance to the next stage.
 * You must avoid getting hit by bullets fired at you by the aliens.
 * The four shields above the surface of the moon absorb shots, both your's and the alien's.
 * You can create a hole in your own shield to fire up through, but alien bullets may drop through the hole as well.
 * As you destroy more aliens, the remaining formation speeds up.
 * The last alien will move the fastest, moving faster while going to the left than to the right.
 * To prevent the aliens from dropping down sooner, concentrate on the aliens positioned in either column edge.
 * If the player's bullet collides with an alien's bullet, one bullet will cancel the other out, and it can be either your bullet or the alien's that continues on.
 * A saucer randomly appears above the formation which you can try to hit for bonus points.
 * Every time you complete a stage and start a new one, the alien formation begins one row lower than before, up to a certain minimum height above the surface.
 * If an alien's path intersects with a shield, that section of the shield is removed.

Saucer scoring trick
To get 300 every time you hit the mystery saucer. It is named the 'Furrer Trick' named after Eric Furrer who perfected it. To do this trick, perform the following :
 * 1) Once the new level begins, start counting the shots from your base.
 * 2) When you have fired 22 shots, stop shooting and wait for the mystery saucer.
 * 3) Use the 23rd shot to blast the mystery saucer.
 * 4) After this, start counting shots again, this time count only to 14.
 * 5) Use the 15th shot to hit the mystery saucer.
 * 6) Continue using the 14 shot rule until the level is finished.
 * 7) At the next wave, start with the 22 shot rule, then use the 14 shot rule to finish that wave.
 * 8) Remember, all shots count regardless of hits or misses.