The second half of the first stage ends with an encounter with the oncoming "comet" which will share the same colour as the planet being defended (blue for Earth, yellow for Venus, Red for Mars, and so on).

If left unhindered, the comet will ultimately collide with and destroy the planet, resulting game over regardless of the remaining stock of player lives.

[3] Mitsuji recounted its development process in a 1988 interview with Japanese magazine Beep, stating that the project originated from a conversation the staff had with the then-president of Taito about creating a title based on Halley's Comet.

[2] Mitsuji remarked that the PCB used for the title was underpowered and had no hardware-scrolling support, prompting the team to work with effort under severe limitations on making the background look as if it was scrolling.

[2] Halley's Comet was first released by Taito in Japan in January 1986 and later by Coin-it in North America on April of the same year.

[14] Likewise, former Toaplan composer Tatsuya Uemura claimed in a 2009 interview that Twin Cobra was influenced by Halley's Comet, as he wanted to portray the feeling of aiming and shooting.

[15] A sequel, Halley Wars is a vertically scrolling shooter released on the Family Computer Disk System in 1991 and later on the Game Gear.