Dark Exhaust

Dark Exhaust is a purple gas that comes from Generals Horse and Bull's cars, which are fueled by Magic Oil.

History
Ever since Generals Horse and Bull have been racing and using Magic Oil as fuel, they have created and spread Dark Exhaust all over the Wild Waste. To anyone who breathes it, the fumes are just a fowl stench, similar to smoke, but it has a different effect on the native Wacti Cacti, turning them into dark, purple versions which spread rapidly across the canyon, damaging or killing anyone unlucky enough to get caught in them.

Plot
Kutaro and Pikarina have a run-in with the cacti morphed by the Dark Exhaust and are chased up the canyon. They eventually escape its grasp and seal it underneath a rockslide. Once Kutaro destroys Generals Horse and Bull's cars, it puts an end to the spread of the Dark Exhaust.