World D-4

World D-4 is the fourth and final level of World D in Super Mario Bros.: The Lost Levels and the twentieth and final secret level overall in said game, as well as the final level in the game overall. Like with World 8-4, lightning flashes in the background of the level and the level's title card in Super Mario All-Stars.

Layout
The player starts in a room similar to that the one at the start of 8-4. The player has to jump across a pit of lava while avoiding a long Fire-Bar, then while avoiding another Fire-Bar at the end of the corridor, the player can find a power-up in a Hidden Block against the wall. Jumping across a lava pit with a Podoboo jumping out and avoiding the next Fire-Bar, the player then has to bounce off of a Koopa Paratroopa and avoid pipes with Piranha Plants, along with Cheep-cheeps that jump out of the lava until the player reaches the next hall. After a falling lift and a Fire-Bar, the player will find a Warp Pipe at the end of the hallway.

The next area is an overworld area, with the first enemy being a charging Hammer Brother. After the second pipe with a Piranha Plant, wind will begin blowing. The player will next encounter two Koopa Paratroopas, two Bloobers, another Piranha Plant, and a hidden Poison Mushroom before a flight of stairs, which the wind will stop blowing beforehand. After a jump across a large pit, the player will find a Warp Pipe with a Piranha Plant.

The third area is a simple underground chamber with coins and a Coin Block above the start of the third row of coins.

The fourth and final area has the player return to the castle, where they will encounter a fake fire-breathing Bowser's Brother (or in the case of All-Stars the actual Bowser's Brother who only throws hammers). Above him is a row of ?s, with the fifth from the right containing a power-up. The next Warp Pipe with the Piranha Plant and Bloobers surrounding it will take the player back to the start of the level. After the pipe is a Hammer Brother, followed by a narrow passage that the player will have to crouch and slide through if they are in a Super or Fire form. Using a lift to get up over a ledge, the player then has to time a fall into a narrow passage while avoiding a Podoboo. Finally, the player will encounter a fake Bowser, who throws breathes fire and has a Fire-Bar above him (in All-Stars, this was replaced by the actual Bowser himself who only throws hammers). Upon defeating him or touching the ax, the player will save Princess Peach and complete the game.