Light Armadillo created these evil Jetmen from their shadows, as they grow stronger, the real Jetmen grow weaker. Maria creates a forcefield of light over the city at night to create daylight so the Shadow Jetman can destroy the city. There were only four, as Gai (Black Condor) was not there when the copies were made. Gai shoots Maria so the light field goes away, the Shadow selves vanish and they can defeat Light Armadillo.
Gai is the only one without a Shadow Jetman because at the time when the Jetmen had their shadows stolen, he was not present. He was about to have a Shadow Jetman when Light Armadillo ambushed him, but his allies interrupted the monster's casting before it could zap him.
The Shadow Jetman share some similarities with the Shadow Rangers from Power Rangers Turbo. Both teams were created from the shadows of the original heroes, had their helmets a different colour from the rest of the suit (albeit reversed, as the Shadow Rangers had uncolored helmets rather than the other way round), had a member missing from the line-up due to their counterpart not being present and were destroyed when no longer exposed to direct light.