Quartet
Double Target - Cynthia no Nemuri (ダブルターゲット シンシアの眠り)
Double Target (더블 타케트)

Level select

Press x12 at the title screen, then hold on controller two, and then press on either controller.

Sound test

Press x4 at the title screen, then press on controller two.

All weapon upgrades

Press x14 at the title screen, then on either controller to start the game with all weapon upgrades (wide beam, longer range, and faster shots).

Action Replay codes

00C2C110

Invincibility (starts with 10980 points, decreases with the time and gets back to the same value when it reaches 9990 points)

00C01603

Infinite lives – Player 1 (keeps showing 2)

00C2C099

Infinite time – Player 1 (starts with 10980 points and it'll decrease only if you get hit)

00C00F0X

Stage select (replace the X on the code for a number from 0 to 5 to go from the first stage to the last stage)

See the main page for Quartet / Double Target - Cynthia no Nemuri (ダブルターゲット シンシアの眠り) / Double Target (더블 타케트)