In Batman: Arkham Knight, the Cloudburst was a weapon that was designed by Simon Stagg under the influence of Scarecrow that launched and amplified the effects of Scarecrow's Fear Toxin. The Cloudburst initially was an invention that was meant to quickly spread cures to diseases in heavily infected areas via inhalation. The Cloudburst ran on Stagg Enterprises' Nimbus Generators, which amplified the Fear Toxin and disabled any vehicles that lacked a Nimbus Cell.
Arkham Knight Incident
On Halloween, the Arkham Knight's Militia took control of Stagg's Airships over Founders' Island. As the Militia began powering up the Cloudburst with Nimbus Cells, their preparations were interrupted by Batman, who infiltrated the airships in search of Scarecrow and Oracle. The Arkham Knight had a chopper rip the Cloudburst from the front of the airship that it was attached to with Scarecrow hanging on, and was forced to finish the power-up offsite. The Cloudburst was then mounted onto the Arkham Knight's personal tank which was well armored and armed. The Cloudburst did succeed in launching the Fear Toxin in Gotham City, and engulfed the entire city to the point that Batman could only fly from building top to building top. It was eventually destroyed by the Batmobile after a long and intense battle with 5 Cobra Tanks and the Cloudburst Tank itself.