Well it depends on what kind of mood im in. If I was in a good mood, I would hop a plane to each of the third world countries with horrible dictators (Kim Jong Il, Fidel Castro, etc.) and kill them, so that there would be peace in those countries, and force the new leaders of those countries to make peace with the world by tricking them into thinking I was the old dictators spirit come back to make amends for all the evils I had done, thus making the world a slightly better place.
If I was in a bad mood, I would kill all the leaders of the world, pin it on another country they each hate, sit back, watch them start wars with each other, and stay on my own private island while the rest of the goes even more down the shitter than it already is.
Of course, I would have a little company in the form of Hawaiian hoola girls or something like that. I may be invisible, but I have needs.