Possible Caustic passive
I know Caustic’s main role is to annoy people and I would argue in the right environment he thrives. However I also felt like there was a little something missing. You’ve got a big, slow legend with no ability to escape. What if, instead of an ability to escape, he had an ability to charge forward. What if after years of working with NoX gas Caustic himself had become toxic to even be in the vicinity of. Essentially giving him a gas aura in a short range around his body as a passive. One that obviously wouldn’t effect team mates preferably. Giving him a last ditch effort ability if he can’t get away, charge in and give him an edge in close quarter gun fights.
