A minor detail that probably doesn't matter much, but I kinda love the cartoony style that you pulled off, while having a smoke effect from the acid that's not really the same style. It works though, and thats what makes it interesting. I'm disappointed with the size of the canvas though; I feel like it was cropped short of something that could have been a really sweet full body piece. But then again, I know I don't have much time for fan art in general, so I could understand.
Great work though, really enjoyed taking in the rust details as well.