Go up the first steep hill until you get to three pipes and a Koopa walking around. Two will have Piranha plants and one will be a Shy-Guy generator. Throw away an egg so Shy-Guys will start jumping out. Kill the two Piranha plants, eat the Koopa and stand on the pipe. Spit the Koopa shell towards the Shy-Guys. The shell will bounce between the two pipes, knocking out the Shy-Guys. As soon as ten Shy-Guys are knocked out, you will start getting a 1-Up for each consecutive Shy-Guy. The shell will keep bouncing around, killing the Shy-Guys that pop out. You can get up to 999 lives this way.