Go to the first T shaped pipes in world 1-2. You need to have a tail so you can float in the air. There will be little goombas coming out of the right end of the pipe. Go on to the ground near where all the goombas are coming out. Let three or four come out before you do anyhting. Then jump on one of them so you bounce up into the air. When you are coming down from that jump land on another one, and after you hit that land on another one. Keep doing this so you never touch the ground. Once you hit one goomba, you will want to flap your tail so that you will provide more time for more goombas to come from the pipe. Once you have stomped on eight in a row, you will get a one-up for every kill on after that.