It was whoever got last hit won the coins, but the devs decided that it wasnt working out the way they wanted it to work. Because we would at some point have a few players stop fighting just stand there and wait for the right time to click and get the 10m over and over and over and over. We had the same person get it 20 times in a row. The devs did not like this, so they changed it to 100% random.