Weird. Why would it change from Sulphur to Vitriol?
If the link is any proof, I'd guess its from the idea that the substance comes from sulphur, and the idea that its a oil-like substance, which was a feature in Litten's fur. The theme may be Heel Wrestling, but I can also see a form of Oil Wrestling
too if everything matches well. As for why it changes to vitriol from sulphur, perhaps it could hint to the alternate forms theory? One represents sulphur, and the other represents the liquid that's vitirol? Of course, I'm just speculating, so take it how you will.
More, just looked up more info of the substance in question from here
, and if I had to guess, the liquid that Litten3 is spitting out in its concept art, may be sulfuric acid
, which is vitirol in question, as well one of the many forms of the substance. Truly a Heel Wrestler, if he's spitting acid into someone's face like that. That and the acid in question as the link describes, is extremely lethal. Clearly, a heel wrestler you don't want to mess with up close and personal.