I'm never very good at questions like these because I get all caught up in the rules of the question like:
a) why do I only have a month to learn this skill?
b) does this mean that some things are barred from the list since it would be impossible to learn some things in only a month?
c) and if not, then why a time constraint at all?
See? It's hard! So, in order to answer this question at all, I'm going to say that it has to be something that I could actually learn in a month, like say, if I were training for a film role. In my super glamorous fantasy life. In this film role I'd have to learn martial arts, of course, so I could kick some ass. (I have watched every BTS featurette for the Charlie's Angels film franchise.)
Also, I'm going to assume my arms with suddenly look like this cause of all the bad assery: