Galaxian (Scott Tunstall's annotated disassembly)

Galaxian counts the aliens still in the swarm, leaving out those in flight, and sets HAVE_AGGRESSIVE_ALIENS when 3 or fewer remain. With the flag set, an attacking alien other than a flagship that reaches the bottom of the screen reappears at the top and attacks again instead of rejoining the swarm, once the player has spawned; before that, it rejoins. Flagships take a separate routine. The disassembly reads the Namco ROM, MAME's galaxian set. galaxian/aggression

About: Galaxian Remaining-enemy speed-up

Value: 3 aliens left in the swarm (threshold)

The same branch also keeps attackers in play when no blue or purple aliens remain (HAVE_NO_BLUE_OR_PURPLE_ALIENS).

Cited by: Galaxian, Remaining-enemy speed-up

Galaxian's swarm holds its formation while aliens break off from it to attack. An array of 8 in-flight slots holds them: slot 1 for a flagship, slots 2 and 3 for its escorts, of which there are at most 2, and slots 4 to 7 for single attackers, so at most 7 aliens fly at once. No attack uses slot 0, which the disassembly's comment says is kept for other uses such as explosions. A single attack scans only $\min (\lfloor (b+e)/2\rfloor ,3)+1$ of the last four slots, where $b$ and $e$ are the two difficulty values, so 1 to 4 single attackers can fly at once. galaxian/attackers

About: Galaxian Enemy formation

{
 "maxInFlight": 7,
 "flagshipEscorts": 2,
 "singleAttackers": [
  1,
  4
 ]
}

Cited by: Enemy formation, Galaxian

Galaxian's difficulty has two parts. A base value rises by 1 with each level cleared, up to 7. An extra value starts each level at 0 and rises by 1 each time two nested counters run out, up to 7. The counters reload to 60 and 20, so once running they step it every 1,200 passes of the game logic, but the cited code doesn't reset them when a level starts, so a level's first step can come sooner. They hold while the player is not in play or after a flagship in flight is shot. The two values set how many single attackers may fly at once and how many attack counters tick. galaxian/difficulty

About: Galaxian Difficulty ramp

{
 "baseMax": 7,
 "extraMax": 7,
 "extraStep": 1200
}

How often HANDLE_MAIN_GAME_LOGIC runs, once per frame or otherwise, isn't read here, so the step is given in passes, not seconds.

Cited by: Difficulty ramp, Galaxian

Galaxian awards one extra ship, a "bonus galixip", when the score's top digits reach the DIP setting: 7,000, 10,000, 12,000, or 20,000 points. A per-player flag then blocks any further award. galaxian/bonus-galixip

About: Galaxian Extra life

[
 7000,
 10000,
 12000,
 20000
]

Cited by: Extra life