Super Mario World/Cheese Bridge Area
One of the first levels with buzz saws. If you activate every one of the platforms it will make it much easier to recover if you take a fall.
The level is much easier if you have a cape and if you use the top platform.
Try flying underneath the real exit with a blue Yoshi or a Mario with cape; you will find another exit which will lead to a secret underwater level called Soda Lake.
HINT: Use regular Yoshi, drop below the normal exit and at the very last second jump off of him. He will fall but you will jump above a platform and find yourself behind the real exit. Yoshi cannot be found in this level and must be brought in from a different one.
HINT: Yoshi can bounce on the buzz saws.