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.

Level statistics

 * Power-ups: 2 (Super Mushrooms or Fire Flowers)
 * 1-Up Mushrooms: 0
 * Poison Mushrooms: 1
 * Secret areas: 0