It messes with your brain. Stops you from tapping into the Force. Nasty stuff.
—Kassie Kaadara.
Zildrog's Breath, named after the mythological dragon god Zildrog, was a gas created by Zakuulan scientist and Knight of Zakuul Judran Mistwood in 23 ATC as a means of destroying the Eternal Alliance and its Jedi leader. The gas had the unique ability to disrupt the neural pathways that allowed a Force-sensitive to tap into and control the Force, preventing them from using their senses and powers and making it an incredibly deadly tool against Jedi, Sith and Force Adepts.
Although typical forms of Force-based poison negation such as Detoxify Poison and breath control were unable to stop the effects of the gas, the Force-neutralizing effects persisted only as long as the gas was in contact with the target, either inhaled or through skin contact, and wore off within minutes when a being escaped the cloud. It also caused a light sensation of nausea and soreness of the eyes, which usually subsided around twenty minutes after exposure. Although initially created as a weapon with which to surprise the Commander of the Eternal Alliance and win the war for Empress Vaylin, Judran Mistwood instead deployed it in select areas against his fellow Knights of Zakuul during the assault on Odessen, both to test its effectiveness in the field and to undermine the brutal regime of Empress Vaylin, who was ultimately killed during the assault.
Later, he sold batches of the gas to various criminal organizations, earning himself a fortune while also allowing the Exchange to establish an operation on Zakuul that rapidly impacted the quality of life of the already struggling Zakuulans. When his involvement in the fall of the Eternal Empire on Odessen and his mercenary behavior in the aftermath became public knowledge, Mistwood was reviled by his fellow Zakuulans and both he and his family became frequent targets of harassment by the time of the Invasion of Ossus in 25 ATC, culminating in a number of vengeful Knights of Zakuul murdering Judran the following year and forcing his family to go into hiding. That same year, the Antiquarians private military company utilized Zildrog's Breath against Loreli Patek and Benjamin Lambert on behalf of the Sith Empire on Dronim Major, bringing about greater awareness of the gas and its effects.
After the successful completion of Operation: Crystal Lekku in 28 ATC, Benjamin Lambert visited Zakuul with his family to inspect the properties he had inherited from his late wife, whereupon he encountered Judran's widow and their young daughter Maris and protected them from the knights who pursued them, enabling them to get off-world. As thanks, Judran's widow gave Benjamin a datacard belonging to her husband that contained the chemical composition for Zildrog's Breath, making him the sole owner of the knowledge required to reproduce the Force-neutralizing gas.
Despite this, Zildrog's Breath that had already been manufactured and sold was relatively widespread and continued to see use over the following decades, most notably by the Antiquarians, who had bought the gas in bulk and made effective use of it against Force users who stood in the way of their aims. Benjamin later entrusted the datacard to Isla Waverunner, governess of Shimka's Well, where a small amount of the gas was manufactured and held in reserve in case it was ever required, and from time to time the Advanced Strategic Operations Service (whose commandos were protected by sealed body armor) was known to employ it against Sith targets.