Star World 3
From the Super Mario Wiki
Star World 3 is the third Star World level in the game Super Mario World which is accessible by the Star Road located to the south of Soda Lake. This level takes place in the sky and features a rare Baby Yellow Yoshi.
Star World 3 consists of one short screen, which the Player has 200 seconds on the Timer to complete. It is made mostly out of Grab Blocks, and grabbing the wrong Grab Block could lead to losing a life. There is a silver P-Switch which can be used to change the Spinies the Lakitu throws at the player into Silver Coins. These Silver Coins can be collected to get many Extra Lives. Like all Star World levels, there are two ways to complete the level.
 Normal Exit
The Giant Gate is directly to the players right at level start.
 Keyhole Exit
To find the Key and Keyhole, the player has to hit the Lakitu with a Grab Block, then steal his Cloud. The player should use the cloud to float up through the opening in the Blocks in the middle, and then float to the left side. To get the Key, the player should hit the ? Block. After the key has been obtained, the player should take the key to the right side of the gap and put it in the Keyhole. Beating the level this way will allow access to Star World 4.