When you start the game, your laser base will be in the bottom left corner of the screen, below the buildings. Your goal is to blast the invaders into dust. Keep in mind that once the invaders make it to either the right or left edge of the screen, they will drop down a row and head in the opposite direction. You should plan your strategy to prevent them from making it to an edge.
A good strategy is to start blasting out the columns on the opposite edge of movement. This is if the invaders are moving right, they start blasting out the leftmost columns first. This way, their return trip is longer and you have more time to deal with them.
Do not attempt to hit the invaders dead center. They fire their laser bombs from dead center and your shots will collide, wasting your shot and letting them move closer to an edge.
Speaking of shots, you can only have one shot out at a time so make it count.
Use your buildings to your advantage. 'Peek' around buildings to get shots and blast a hole in the middle of your buildings to give you protection while you knock out columns of invaders. Keep in mind, this protection will only last about two columns before the invaders blow open a hole wide enough to destroy your laser base.
Every other wave of invaders starts one row lower. Eventually, the waves will start one row above your buildings. Be prepared to do some fast shooting to keep them from getting any lower because once they reach your level, the game is over.
When you are down to taking out the last invader on a wave, that invader will zip across the screen. The strange thing is that the invader travels faster going left to right than going right to left. Keep this in mind when trying to shoot it.
The mystery saucer (or UFO) will appear at random times. If you have a good shot at it, try to hit it. Don't go out of your way, however, to go after it; it isn't worth the risk or time wasted.
The Hidden Message Trick : To get the hidden message, you must do the following :
1) When the demo starts, you need to press the following keys at the same time on the machine : LEFT, RIGHT, FIRE, 1P START, 2P START.
2) Continue to press these keys rapidly as fast as you can.
3) If you are successful, the message ('TAITO CORP') will appear under the high score.
Shot Counting 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.
Eric Furrer writes : Here's a variant of the Counting Trick that most people don't know and it's the exact trick I used to play that darn game for 36 hours over 20 years ago. The shot count trick works great for level 1,2,3 but you can't use 22-14-14 counts for mystery ships on the 4th wave because the invaders are too low. If you wait around for the ship after 22-14, then the invaders will be down too quick and you will surely die. Most players at this point do a 22 count and abandon the remaining 14 counts and just clear the board. This slows point accumulation.
My solution is simple and the shot count works in progressions as well : On the 4th wave count 22, wait, and clobber the 300. Now instead of counting 14, shoot the 29 invaders in the bottom rows and get the ship. Now the invaders are high enough to do two more 14's.
Here's the grid for rolling the machine's score in about 6 minutes by the forth wave using 29. Otherwise, you'd have to wait until the 5th wave. Seems minor, but it saves 30 seconds per roll, which could mean a 30 minute lead against a good player on a head to head speed match, a difference of about 50,000 points!
1st wave - 22, 14, 14, 14, 14, 14 (bonus = 3000 + 990 = 3990 first wave)
2nd wave - 22, 14, 14, 14 (bonus = 1200 + 990 = 2190 total score now = 6180)
3rd wave - 22, 14, 14, 14 (bonus = 1200 + 990 = 2190 total score now = 8370)
4th wave - 22, 29, 14 (bonus = 900 + 990 = 1890 total score now = 0260 or 10260) (if you counted 22, 14, you couldn't get the 3rd 14 without severe risk of death row)
5th wave - 22, 29, 14 (same as 4th wave)
6th wave - 22, 14
7th wave - 22 14
8th wave - 22
9th wave - 22
Then back to the first wave!!