Killscreen is a point pressing version of Galaga, where final score is taken at the end of Stage 255. This completes one full loop of the entire game, after which it goes to Stage 0 and either crashes or loops depending on the settings (see below)
This mode can be played on any difficulty and life settings that were available on the Arcade version of Galaga (Rev B). Fast Fire is allowed, though its use is noted and is an open question of if it should be measured together or separate. One the one hand, it can help a player that could otherwise not reach Stage 255 get there and improve some Challenge Stages. On the other, it is much harder to point press, and a top score will be prohibitively more difficult to obtain. Typically Normal Fire scores run higher.
The most common settings are 3 lives + 20,000/70,000/70,000 on Rank A/Easy, Normal Fire speed, and are assumed as default if not otherwise noted.
Also goes by: Single Loop, 1-loop, 1cc (1 credit clear), etc.
Stage 0 outcomes based on Rank/Difficulty setting:
Rank A/Easy – The game crashes on Stage 0. This is the ‘killscreen.’
Rank B/Medium – Stage 0 is a very strange combination of a regular stage and a Challenge Stage. Then, the game loops.
Rank C/Hard – on Stage 0, no enemies ever come out, effectively ending the game. A different, but equally game-ending ‘killscreen’ to Rank A.
Rank D/Hardest – Stage 0 slows back down, and plays mostly like a regular stage and the game loops forever.
Even though B and D loop, the score after Stage 255 can be used as the effective “killscreen” score.