Tranquilizer guns are projectile weapons primarily used to fire a chemical to sedate others.
"Awakening Part Three"
Xanatos’s commandos shot Goliath with a tranquilizer dart in Central Park.
"Awakening Part Four"
While the commandos chased Elisa, she was able to get one of their tranquilizer guns away from one commando she tripped and shot another commando with it.  The female commando tried to shoot Elisa with a tranquilizer dart, but missed.
"Long Way To Morning"
Demona broke into Elisa’s apartment and used a projectile gun similar to the tranquilizer guns to fire a poison dart at Elisa. Elisa’s badge blocked the dart.
When Maggie escaped from Gen-U-Tech, she was spotted by Brooklyn and Broadway on patrol. Xanatos’s commandos arrived and tried to tranquilize all three. Maggie surrendered and Brooklyn was hit by a tranquilizer dart in the back, prompting his and Broadway’s retreat. Sevarius later used a tranquilizer gun to fire a projectile at Derek Maza, but it was the mutagenic formula and not a sedative. Maggie was hit by tranquilizer dart fired by one the commandos when Goliath, Brooklyn and Lexington broke her out of Gen-U-Tech.
"Eye of the Beholder"
Xanatos shot Fox with a tranquilizer dart in her werefox form. She pulled out the dart and swatted the gun out of his hand. Owen then entered and shot her with a second dart. Due to her enhanced state, neither dart seemed to have an effect on her.
When Sevarius’s mercenaries brought a sleeping Thailog to him, Sevarius had a tranquilizer gun at the ready. It is unknown if he used it.
After his ninjas failed to defeat Elisa, Taro knocked her out with a tranquilizer dart. Later, when Kai tried to leave the Gargoyle Theme Park with his clan, Taro did the same to him.
"Hunter's Moon Part Three"
To protect Elisa, Jason Canmore scooped her up on his sky-sled. To keep her from struggling, he tranquilized her with a jet injector.
Sevarius was preparing to tranquilize Robyn Canmore, so he could inject with mutagenic formula with gargoyle DNA taken from Angela, when the gun was knocked out of his hand by Dingo.
The tranquilizer guns came in all sizes. Sevarius, Demona, Taro, Xanatos, and his commandos used a handheld gun. However, the commandos once used a rifle that could fire particle beams as well. As stated above, Jason Canmore used a jet injector.
Although primarily used for sedatives, other chemicals could be used, as in Demona and Sevarius’s case, poison and mutagenic formula, respectively.
How the sedatives affected those injected varied. Elisa, a commando, and Kai fell unconscious within seconds. Goliath and Brooklyn were able to stay awake until their next stone sleep. Fox in her wereform was not affected at all. Greg Weisman muses that the effects on Goliath, at least, in his first encounter with the Xanatos's commandos was inconsistent simply because there had never been an opportunity to test the sedative on a gargoyle before.