World Mushroom-1 (New Super Mario Bros. 2)
From the Super Mario Wiki
Mario starts off in between two ? Blocks, the right one containing a Super Leaf. A Goomba then appears, followed by several green Koopa Paratroopas. Below them are two Brick Blocks, one of which contains many coins. More Paratroopas follow. After that, there is a stack of colored blocks in between blue and red Warp Pipes (the red one is infested with a Piranha Plant) having Goombas and red Koopa Troopas guarding a yellow Warp Pipe below the structure. This is followed by the checkpoint. More stacks of colored blocks follow along with several Koopas, Paratroopas and Goombas. Above the stack is a Gold Ring. This is followed by another stack of colored blocks which is arranged like a maze. A lone red Koopa and a Red Ring can be found there. A yellow Warp Pipe can be found at the bottom of the stack. Another Piranha Plant follows. Further down the level, there are two tall stacks of colored blocks followed by several Koopas and Paratroopas. Three pipes of ascending heights, the second with a Koopa and the last with a Piranha Plant, comes at the end with the flagpole.
The entrance to the secret exit is located to the left of the third Star Coin near the end of the level. The player needs to locate a hidden block on the left stack of boxes which contains a Beanstalk. The Beanstalk leads up to an area with four ? Blocks, three of which are flying. Many green Paratroopas are active in the area, some of them partially enclosed by Brick Blocks. Three flying ? Blocks and a Paratroopa follow. Lastly, the flagpole appears, which takes the player to the desired levels.