For each enemy you stomp without touching the ground, you'll earn more and more points, and eventually 1-Ups. The score for each enemy stomped will be: 100, 200, 400, 800, 1000, 2000, 4000, 8000, then 1-Ups for each enemy thereafter. Remember: Fences and vines don't count as ground! Similarly, when you kill enemies with a Shell, from invincibility, or when you go through Goalposts, the score for each enemy increases the same way. But when you activate a Gray P-Switch, Gray Coins collected will increase up to 8000 points, then a 1-Up, a 2-Up, and 3-Ups for any more you get.