World 4-Ghost House (New Super Mario Bros. 2)
From the Super Mario Wiki, the Mario encyclopedia
Mario begins in front of three moving ? Blocks. A Boo begins to follow. Further down are two ? Blocks, one of them containing a Fire Flower. To the right is a fake door. Going up the stairs leads to the real door, taking Mario to a room where the walls are 'driven' by several Boos. Moving forward are some stairs and another fake door. There are then several platforms on the floor which rise or lower when Mario stands on them. This is followed by two ? Blocks, one of them containing a Super Leaf. The Boos then 'drive' the walls in the reverse direction for a short moment. Following the ? Blocks is a Red Ring. Mario then has to climb several platforms and drop down a small shaft before getting crushed by the walls. Mario will then come across two ? Blocks containing coins. Following that is a P Switch, which makes Blue Coins appear. After that there is a structure which Mario has to climb before getting crushed by the walls. At the top is the door leading outside. A Boo and a Springboard can be found, followed by the Goal Pole.
After the area with the platforms that rise and lower early in the level, there are two ? Blocks, of which one of them has a Super Leaf. After the Boos reverse and return to their normal direction, climb above these blocks and when they are about to go offscreen, quickly wall kick between the two Boo-driven walls to find a secret door. Quickly enter the door and continue on to find the flagpole.
This exit unlocks World 4-B.