What is this?

So, there’s a horror movie that I can’t remember the name of. I’m hoping someone in here might be able to help me out. All I can remember is this chick wears some sort of mask, maybe a gas mask of some kind? She goes around killing folks in some pretty brutal manners. Oh, and her tits are out pretty much the entire time. I think there might have been a 3 in the title. Any ideas?

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