Sure, I mentioned that Tom Kyte shared something about invisible columns but I do not think that I read the post he linked to which did go a bit deeper into the subject. I bring this up, because I found a pretty good article that walks us through several scenarios around making columns invisible in 12c.
Do you know if a column can be selected if it is marked as invisible? Are there any pitfalls you need to avoid when changing this property of the column? If you aren't sure of the answer to these questions, go visit the article from Rajesh and learn something new this weekend!