Dragon Ninja is a song from Bad Dudes. It plays during the boss battles on each stage except the first since the first boss, Karnov, has a custom boss music based on the music from his game.
The official title come from the Deco History: Data East Game Music Scene One album where the song is named 電光石火 (Ryu no Ninja) which translates to "Dragon Ninja," the name of the game's ultimate villain.
Bad Dudes vs. Dragonninja (ARC)
This is the original version of the song. It is rendered on the game's YM3812.
Dragonninja vs. Dragonninja (AMI)
Bad Dudes (NES)
The Dragon Ninja music plays in the same stages as the arcade version, only it's more perceptible in the NES port.
The song is track 4 in the NSF file.
The Amstrad, C64, and Spectrum ports have different soundtracks that don't include this song. The Apple II, DOS, and MSX ports do not have music.