Yellow Switch Palace

The Yellow Switch Palace is a level in Super Mario World that contains a giant yellow ! Switch. It is the first Switch Palace that Mario and Luigi find, as the palace is not hidden. It is on top of Kappa Mountain in the northwest of Yoshi's Island, and it is accessed by completing Yoshi's Island 1, thus making it the only Switch Palace that the player does not need to find a secret exit to access. The entire level contains no enemies or power-ups (and is the only Switch Palace to do so), and it cannot be replayed after it has been completed, at least without the aid of an exploit in Super Mario World: Super Mario Advance 2.

Overview
The palace consists of two rooms, which the player has 200 seconds on the timer to complete. The first room of the palace is a large open area with a single Switch Block. When the switch is hit, the room gets filled with about 500 coins, and the player has about ten seconds to collect as many as possible; however, the player is not required to hit the Switch Block to progress through the level.

A Warp Pipe guides the player to the second room, which contains the yellow ! Switch. The player can simply jump on top of it to activate it and end the level.

Gameplay effects
Once the yellow ! Switch is activated, all the yellow Dotted-Line Blocks turn into Yellow Blocks. During gameplay, a Super Mushroom appears when a Yellow Block is hit. These blocks also help the player progress through levels by filling in some gaps. The Yellow Blocks appear in only 21 levels after that.

Levels with Yellow Blocks
Yellow Blocks can be found in 21 levels:
 * Yoshi's Island 1
 * Yoshi's Island 2
 * Yoshi's Island 3
 * Yoshi's Island 4
 * Donut Plains 1
 * Donut Plains 2
 * #2 Morton's Castle
 * Vanilla Fortress
 * Forest of Illusion 2
 * Forest Fortress
 * Chocolate Island 1
 * Chocolate Island 2
 * Chocolate Island 4
 * #6 Wendy's Castle
 * Valley Fortress
 * Valley of Bowser 1
 * Valley of Bowser 2
 * Valley of Bowser 4
 * #7 Larry's Castle
 * Front Door
 * Star World 5