Mystery of the Castle?

Mystery of the Castle? is the Secret Stage of World 2 in Yoshi's Island: Super Mario Advance 3.

Layout
The level starts out with Yoshi going right-to-left over a few long pits of spikes, while avoiding several Fangs. After that, the player finds an Egg Block and a Warp Pipe. After going through the Warp Pipe, the player finds a hidden Winged Cloud, and a maze of bridges over lava. Eventually the player finds a Middle Ring.

Eventually through the maze, the player finds a Warp Pipe going upwards; Once the player go through the Warp Pipe, they have to choose one of the two ways to go, a door and another Warp Pipe. The door is out of reach so the player needs to bounce on a Zeus Guy. After going through there, they are able to throw an Egg to break a rock on the ceiling, causing an spinning wheel to fall down, allowing them to bounce up to a platform with hidden coins. Then, the player goes back down, and through the Warp Pipe.

Through it, there is another Middle Ring. After crossing some spikes, the player continue upwards, riding Flatbed Ferries, until the player winds up in another maze of bridges. Through that, the player finds some rocks they need to throw eggs at to break, and after breaking them, the player can go through a Warp Pipe. The player then winds up at the end of the level.

However, the player can get a key, somewhere else through the maze, and ride a spinning wheel to get up to a locked door. Upon entering that locked door, the player finds a Middle Ring. The player then needs to cross a long gap of thorns. After that, the player goes down a long shaft, at the bottom, they need to cross a pit of spikes. After crossing it, they find a few ways to go, with one of them being a door that takes the player back to the maze area. Instead, the player must ride a spinning wheel upwards, and across a pit of spikes, in order to reach an area where they can Ground Pound a breakable rock, and get to a door.

Upon entering the door, they find a ! Switch. The player can hit it to make ! Blocks appear so they can cross a pit of lava. After crossing the pit, they get to a door, that takes them back to the shaft they went down earlier. If the player keeps going this way, they are stuck in an endless circle, so the only reason to go around that way is to get extra points and items.

Enemies

 * Bandit
 * Dizzy Dandy
 * Fang
 * Lava Drop
 * Grunt
 * Green Glove
 * Grim Leecher
 * Koopa Troopa
 * Solo Toady
 * Zeus Guy