Galaga 3 is a sequel to Galaga and has similar gameplay. The player controls a spaceship, that can now move vertically (limited to halfway up the screen) as well as horizontally, and shoots at swarms of incoming insect-like aliens which fly in formation above it and swoop down to bomb it in a kamikaze-like dive. In this sequel, the level starts over if the player is killed before all the enemies have come in. When all enemies are destroyed, the player moves on to the next level. By obtaining certain power-ups, it is possible to shoot 60 bullets per screen, the most any Galaga related game has.
By shooting at a shooting star that occasionally appears, the player can get a ship with new graphics that can have three shots on screen instead of two. After this, shooting the star will make a special flag appear from the Namco game Rally-X that awards an extra life when collected. On certain levels, the motion of the starfield reverses. This is accompanied by enemies attacking in waves, leaving the playfield if not shot. After this, a small force appears in formation as in a normal stage.
The challenging stages are different from those in Galaga. Enemies are juggled by shooting them, each hit slowly spelling out (in order as the game progresses) “Bonus”, “Gaplus”, “Double”, “Triple”, “Good!!”, “Lucky”, “Bye Bye”, and “Extend”; shots that hit enemies after the word has been spelled out each award an extra 200 points. It is most effective to use the red and blue powerups to repeatedly hit them.
Some challenging stages have an additional bonus awarded after the word has been spelled and the bonus calculated. For example, on a challenging stage where ‘Gaplus’ is spelled out, the player is instructed to press the fire button for an additional bonus; the award is between 10,000 and 50,000 points in multiples of 10,000. On the level where ‘Lucky” is spelled, another bonus ship piece is awarded; on the ‘Bye Bye’ level, a bonus ship piece is taken away.
The “Boss Galaga” from Galaga returns as the Queen Gaplus, a single enemy that sits at the top of the alien formation. It typically carries an item which can be obtained when it is destroyed before it leaves the screen. One type of item is a series of ship upgrades called “Blaster Heads”, which are as follows: the red Phalanx captures enemies with a tractor beam where each one provides another shot; the blue Hyper gives wider and faster shots, an upgraded version of the “dual” ship from Galaga; the green Cyclone captures enemies in a tractor beam that can then be shot for bonus points; the purple Elephant is temporary and slows all enemies down, but not their bullets; the grey Sidewinder allows you to direct your shots left and right as they move; finally, the rare yellow Stardust is temporary and turns enemy bullets into harmless stars. All of these powerups may be stacked on top of one another, greatly increasing the player’s maximum firepower. If the Queen does not have one of these powerups, she may instead carry one of three parts to the player’s ship. When obtained, these parts are placed in the lower-right of the screen; an extra life is awarded when all three are collected.
Galaga 3 can be played by a single player or by two players alternating turns. The factory settings start the player out with three lives, a bonus life at 30,000 points, 70,000 points, and every 70,000 thereafter on the easiest level of play.