World 8-4 (Super Mario Bros.)

World 8-4 is the fourth and final level of World 8 in Super Mario Bros., as well as the thirty-second and final level in the game overall.

Layout
The final castle level consists of several Warp Pipes leading between rooms. One pipe in each area takes the player either to the next room or back to the start. If the player does not take the pipe, the room will loop around.

In the first area, the first Warp Pipe the player comes to is the pipe the player will exit from if they take the wrong ones up ahead. The next pipe will lead back to the start, and the pipe after that across a lava gap with a lift will lead to the next area. In the second area, the second pipe from the one the player exited from leads back to the start. The floating pipe up ahead leads to the next area, a Hidden Block is placed to the left of the pipe that acts as a platform to reach the pipe. In the third area, Cheep-cheeps will start jumping up from below. The second pipe from the one the player exited from leads back to the start. The pipe immediately after across a lava gap will lead to an underwater area with Fire-Bars and Bloobers. The pipe at the end of the underwater area leads to the final room, with the only other pipe leading back to the start. After a Hammer Brother followed by a Podoboo, the player will face Bowser, who throws hammers and breathes fire at the player character. Defeating him or touching the axe to destroy the bridge will allow the player to rescue the princess and complete the game.

Super Mario Bros. Deluxe challenges
In Super Mario Bros. Deluxe, the player can collect five Red Coins, find a hidden Yoshi Egg, and get a medal based on their score. The Yoshi Egg is found in a Hidden Block directly above the pipe the player exits from in the underwater area, and the score to beat is 18000. The Red Coin locations are:
 * Directly above the stairs at the start of the level
 * Over the lava pit in the first area
 * High above after the pipe the player needs to progress through in the third area
 * Above the third Fire-Bar in the underwater section
 * Above the axe at the end of the level

Trivia

 * Minor changes to the soundtrack occurred between the original NES version and the All-Stars version; in the underwater section of the NES version, the music switches from the castle theme to the underwater theme, while the All-Stars version keeps the castle theme for the whole level, until the player battles Bowser. In the All-Stars version, the boss theme is different than fighting the False Bowsers in the other seven castles.
 * Despite the original level having 16 vertical pipes, only 14 Piranha Plants can be seen. The pipe at the end of the first area is empty due to the maze loop, since the player appears to take a "wrong" path before reaching the correct warp pipe, while the underwater area begins with a pipe that has an invisible Piranha Plant due to a graphical glitch. Both problems are fixed in the All-Stars version, and Piranha Plants can be seen in all 16 pipes.
 * The ending portion of the level makes a cameo in the Mario Clock app after the player gains 1200 coins.
 * The tileset used for the underwater section for this level is basically the normal castle tileset but recolored lime green like the tileset for the normal underwater theme. It is also currently the only tileset from the original Super Mario Bros. game to not be featured in the Super Mario Maker games.

Mondo 8-4 (Super Mario Bros.)