The level starts in a long corridor with boos and ? blocks. As you approach the second ? block, it will split into two. The left block will contain a Super Leaf. Once equipped, go in the doorway.
Soon after going through the door, you will be confronted by the massive Boohemoth! It will slowly follow you throughout the stage, much like a Boo. You can only advance while it remains on the screen. However, you can temporarily stop it by facing its direction, much like a regular Boo.
You'll soon see a regular Boo by a brick, which can be turned into a Gold Brick for coins and protection. Past it is a moving platform, which must be rushed through. On the other side, the ground is bouncy, sending Mario up into the air. As you see platforms ahead, stay on top of them and jump over the top of the wall ahead to get the first star coin. Soon, you'll come across a platform that slowly collapses under your weight. Wait till it fully collapses, then go right to collect the second star coin. The Red Ring, whose red coins can easily be collected, grants a Super Leaf. As soon as you see a slightly higher portion of the floor, bounce on it in place and wait for the third and final star coin to pop in.
After the final star coin, continue jumping ahead onto the rotating platform and go through the doorway. Attempt to go into the first two doorways you see, avoiding the Boo along the way. Although this won't work, it is necessary. Once done, go to the bottom right platform and stand on it to reveal the real door. Once you go through it, it is a short jog to the flagpole.
Secret Exit[edit]
On the lower step after the flagpole, there is a hidden block you can jump up to hit. Hitting it reveals a hidden vine, which can be climbed up. Continuing along this new path will reveal a new flagpole, and with it a Mushroom House and 2-B.