Closely resembling the Assault Trooper, the Firefly Trooper is modeled on a humanoid lizard with brown skin and black stripes. Like the Assault Trooper, it has three digits on each appendage and wields a gun in its right hand. Unlike the Assault Trooper, it has large green eyes, white and red armor, and a relatively slender build.
The Firefly Trooper is armed with a flamethrower that can kill the player in seconds, and it has the ability to shrink itself while flying in the air. While shrunk and flying, it sparkles, mimicking the appearance of an actual firefly. Like the Assault Trooper, it has a jetpack, but it only uses this while shrunk. If the player is too far from the Firefly Trooper, then it may enter a special firing state during which it fires Incinerator projectiles while remaining partially shrunk and suspended in the air. The Incinerator projectiles coalesce into pools of lava on the ground. At close ranges, the Firefly Trooper may also crouch and fire a red laser projectile, similar to the Assault Trooper's.
Given its short-range yet high-damage weapon, the Firefly Trooper is most dangerous in close quarters. This danger is compounded by the fact that, when killed by any weapon other than an explosive, the Firefly Trooper briefly flashes red before exploding. The Firefly Trooper's detonation is among the most dangerous in the game, dealing twice as much damage as detonations of the Sentry Drone or Pig Cop Tank.
The Firefly Trooper has slightly more health than the Assault Trooper and can be killed with a single blast from the Shotgun. While shrunk, it is invulnerable to all munitions except for explosions. Moreover, the Firefly Trooper is always immune to the Shrinker.
The Firefly Trooper was created using alternate sprites for the Assault Trooper that were scrapped before the 1996 release of Duke Nukem 3D. These alternate sprites were publicly known as far back as 1996, when one sprite was accidentally leaked on the back cover of the Duke Nukem 3D Screen Saver & Entertainment Pack.
Nerve Software obtained the full set of sprites from Richard "TerminX" Gobeille,source who signed a non-disclosure agreement and was given the complete archive of Duke Nukem 3D development files in 2014.