Cyanogen

Cyanogen is a gas that poisonous to nearly all those who breathe it except one species, the Celegians who thrive on it for survival.

It was an important factor in the defeat of Nago Sadow's Massassi forces on Kirrek during the Great Hyperspace War. The Celegian Jedi Ooroo sacrified himself by tipping his chamber filled with cyanogen into the Massassi, killing many. He broke loose and was subsequently poisoned by oxygen.