I finally got this on 3-3 The Revolt. I completed my first playthrough trying to take out any flyers with grenades. However, most of those were while I was hovering, which I do not think counts. Then when I went back to mop-up - I was doing the first part of 3-3, because I was trying to get Float like a butterfly. There happened to be 3 or 4 of the flyer guys so I started chucking my grenades. After the 3rd attempt it popped. I think you have to accumulate more than 10 of these grenades kills.
FYI - Once you kill everyone in this room it saves, so you can safely quit. Although I think it saves most of those stats anyways.
Now time for some grinding...hopefully I understand the method of doing grease monkey properly.
Last edited by big red marino; 05-04-2010 at 05:56 PM.