Alternate Stance

[T.O.R.N.A.D.O]

Well I am currently developing a character who is immune to fire (basically fire heals him). But I don't want to directly implement it. I want to create an alternate stance in which he will be immune to fire. So what I want is upon pressing certain combination, say DJ for ex, he should go to an alternate stance. And while in that stance when hit with fire attacks, he should go to certain frame numbers where he will do the healing animation and heal himself. So can anyone here tell me how to code it?