Revising all the time is making me slide towards being an INTP again, however, I will add my 2c on this matter anyway;
I've always believed that in times of growth and stress we move towards our weaker functions, either becoming more well rounded individuals or complete and utter trainwrecks.
In growth, we grow in confidence and happiness and hence tend to move out of our own mental comfort zones, using our weaker functions to a greater extent than we normally would. This doesn't mean that we turn into our 'shadows' however, it just means that as individuals our weaknesses appear more balanced out; the weaker functions only ever act to supplement the stronger ones, never to overtake them.
On the other hand, in stress we tend to abandon our stronger functions, slowly pushing down the list to find something which 'works'. Of course, our weaker functions are still in an immature state so usually strange behaviours begin to exhibit in the individual; to put it simply, its like putting a two year old with ADHD in charge of a candy store. Yeah, not good.
In shadow ENFJ form, I become pretty much engulfed by whatever angry feeling which I'm feeling - I move from a state of near-constant apathy to constant emotion. I allow these feelings to control my actions. I tend to diriect these bad emotions at the nearest possible outlet - myself.
A ENFJ in shadow form would most likely become detached from his/her emotions, often to the point of obsessively trying to find logic in situations where there is none. I can't speak so much for that one however ^^