Galaga is an extremely popular and successful arcade game created by Namco. The gameplay borrowed from Space Invaders by pitting a single human controlled ship against a fleet of what could quite possibly be alien space ships who "Increase speed, drop down, and reverse direction." The game is a sequel to the highly successful arcade game Galaxian and is followed by both the less successful Gaplus and the highly innovative Galaga '88.
What made it unique from Space Invaders besides the colorful interface was the use of bonus stages and the way enemy ships would fly in at a round swooping formation, a staple of most Shmup games since. Since it became an arcade classic, Galaga has been ported to the NES, Atari 7800, Game Boy, and Mobile phones.
Galaga is similar in gameplay to Galaxian in that the player controls a ship at the bottom of the screen, shooting at an arrangement of aliens at the top. However, it deviates from Galaxian in the following aspects:
- The aliens no longer simply materialize at the top of the screen; instead, they make a swirling path entrance from the sides of the screen in five groups of eight and enter their positions in formation.
- One of the aliens, the Galaga Flagship, requires two hits to be destroyed. Also, on occasion, one of them will stop in midflight and hover over the bottom of the screen while emitting a tractor beam which, if the player's ship is caught in it, will beam it toward the flagship and fly in tandem with it, changing from white to red. If the player shoots the flagship that has the captured ship while they are attacking together, the captured ship will change back to white and then hook up to the player's current ship, forming a doubleship that gives the player increased range and firepower. However, the doubleship also becomes a bigger target for the divebombing aliens, since either or both ships can be lost at the same time.
- On Stages 3,7,11,15,19, and every 4th stage thereafter, the player enters a Challenge Stage where five groups of eight aliens move around in swirling paths on the screen and then disappear without threatening the player. During this time, the player can destroy as many aliens as he can until the stage ends. When it ends, the player is awarded 100 points for every alien destroyed. If all 40 aliens are destroyed, the player earns a 10,000 point bonus.
- From Stage 4 onward, one of the lower-rung aliens will split into a trio of aliens that, if all three are destroyed, will earn the player bonus points. One of the forms of that the alien trio takes is that of the Galaxian flagship.