Toxina sneaks into a bank but then triggers the alarm as a huge cage drops on her as the alarm turns on. She also knows that her horrible No-face is what will get her out of it, so when she removes it, the toxins start making everything decompose because of the toxins on her face.

" I am sure anyone would die if they looked at her, and it might not be the toxins."

So yeah, this is Toxinas real face. Not pretty but affective, its the reason why she keeps her first mask on, because it keeps her pretty, the 2nd hides her identity and the smell, plus her face might melt away the money she needs to steal.