Super Mario World/Donut Plains/Green Switch Palace
You start out in a room with a P Switch, a Tornado Shell, brown blocks, coins, and Koopas. Hit the switch and run across the coins that changed into blocks. The Tornado Shell will hit all the Koopas and get you a 1up! Then get it in between two coins before the switch runs out. This will trap it. Go through the pipe and press the Green Switch. Now you will find green blocks. These give you a cape if hit, and they make it easy to unlock DONUT SECRET 1. You need them to get past STAR WORLD 4 along with red blocks, and you need them to enter the Special World.