On this question of the shadow functions... couple a things:
we're talking functions that exist in you in the same order as normal, but with the normal focus reversed. I can sort of see it being true. If you normally rely on say dominant Ni and auxiliary Te, and some kind of substantially stressful situation is upon you, a situation where your normal function is incapable of producing a result, but you have to produce a result, then the normal functions hunt around for another way--they reverse, perhaps. Why wouldn't they? They're already there, they function and produce a functional result, why wouldn't they under extreme stress (1) try to be themselves, but (2) look for a different expression, a different result, a different focus... if they really had to.
Like if you know how to use X to solve X types problems, but you get a Y type problem and you really have to solve it, you still use X but with a different application.
But they don't reverse to produce normal, healthy functioning. They can't, because, being rarely that way focused, they're so low powered. So, if they reverse, they do it relying on past achievements of the normal functions functioning normally.
So, if I go ENTP, it's with an Ne and Ti that already has a clear map of the world from normal Ni/Te functioning. I wouldn't go ENTP to be ENTP but to support the ailing INTJ I really am. See what I mean? Mostly the shadow would be defensive and aggressive.
The times I believe I have put on an ENTP face:
1. To teach class (because the classes I teach are not straight lectures--I am, of all things, an EFL instructor.)
2. To deal with Fe users that have me intimately cornered
3. any public meeting, maybe.
What happens? Well...
In intimately benign but nonetheless stressful situations, like class, I pose and strut to get laughs and get students on my side, because they have to be happy and jolly or they won't join in the activities I have to make them do. I use non sequitur humour, and poke fun at feelings. I say random things. I discover random connections or surprising developments of ideas. (And then I bear down with hardcore INTJ "Do X now" style instructions.)
In intimately stressful situations, I tear up the place with really aggressive proofs of how and why other people have transgressed. I focus outward to bluntly coerce. And I chop and change too. I can't sustain that digging away at other people for long, so after a burst of logic display, I drop back into low voiced observations, without humour, in fact often deeply grim, in fact.
In public, anytime, if I'm confident of being at least a little bit dominant, I'll almost always have a burst of energy at the beginning of interactions with others. It'll include T-type boisterous joking around, usually observational, focusing on absurdities. It gets worn out pretty fast.
Yeah, it all sounds like being a prick, but, hey--it's ENTP.
Alarming conclusions: so... those strange non-duality relationships you hear so much about... INTJs with INFJs or INTPs, or INTJs with ENXJs... and so on... they love you best when you're stressed, because when you're stressed you look much more like their dual.:horor:
INTJs and INFJ particularly. Stressed INTJ is a perverted ENTP, and stressed INFJ is--oh, my god--a whacked out ENFP.
Ain't love grand.