Super Sentai Villains And Death Gas Plots!
Here's some Super Sentai moments where poisoned gas was used as a main plot or not... though this list I assume is pretty incomplete so feel free to throw in your comments on what I missed.
In Dynaman episode 47 (now only if I saw more of Dynaman than just some raw videos and the Dynaman parody dub), there's the Poison Gas Weasel monster. He was created to poison people but according to Power Rangers Wiki, the gas got tainted by the Retro Gene created by Professor Yumeno resulting to rather hilarious consequences.
In Bioman episode six, Dr. Man plans to set a rather genius trap that involved Mt. Taikyoku and having an underground trap. Dr. Man knew he can't face Bio Robo head on so he has Farrah create a trap that would release poison gas into the air. It was revealed to be a trap for Bio Robo from the beginning to the end of the episode.
Maskman episode 29 had Death Gas Dogra released as part of Emperor Zeba's plan to poison humanity. Now that the Maskmen are without a team cannon, the monster was sent to turn Tokyo into a city of death so Tube could invade the surface world. The Maskmen's team engineer wanted to complete the new weapon since he was a victim of the poison gas plan so many years ago!
In Gingaman episode 7, Sanbash tries to revive Daitanix with the use of poisonous gas, considering the monster was born from a poisonous planet. This episode had the whole of Japan poisoned but the Starbeasts sacrificed themselves to save everyone. In the next episode, the Gingamen finally unleash the power of the Starbeasts to unite into the Gingaioh.