In World 6-3, stand on the gray platforms after the first two pulley lifts and keep jumping on the Bullet Bills that fly by. Sometimes, the Bullet Bill you stomped will stay alive, and a line will appear above it. If you're lucky, the Bullet Bill will stop in midair! Mario can bounce on the motionless Bullet Bill to make it descend slowly, and the line will get longer as the Bullet Bill goes lower. The stopped Bullet Bill will fall if you scroll the screen a little bit to the right.

Note that no points are awarded when the Bullet Bill survives the stomp. This glitch appears to be caused by the nearby pulley lifts.