World 1-2 (Super Mario Bros.)

World 1-2 is the second course of World 1 in Super Mario Bros. It is the first underground level, and it holds the infamous Warp Zone, which, if done correctly, the player can use to enter Minus World.

Layout
The player starts the level by falling through a hole in the roof by a pipe. There will be two Goombas and five Question Blocks. The first one contains a Super Mushroom or Fire Flower, the other four ones contain coins. There will be a block tower structure, where there's a Goomba and a Brick Block with 10 coins. Ahead, there will be some Brick Blocks, one of them containing a Super Star and some Coins, with two Koopa Troopas underneath them. The player will reach a place filled with Brick Blocks with a Koopa Troopa and five Goombas. There will also be a Brick Block with a Super Mushroom or Fire Flower and a masked Brick Block with ten Coins. There will be a Pit and, after it, a Block platform that allows Mario to get an 1-Up Mushroom. The player will find two Goombas and three pipes, all of them containing Piranha Plants. The player can enter in the first Pipe, that will lead them to a room with Coins and a 10-Coin Brick Block. The player can exit the area by a Warp Pipe in the extreme right. This pipe will lead to the third one in the main area. There will be two gaps and, between them, two ground blocks and some Brick Blocks. After that, a small, half-pyramid structure with two Goombas is seen. Ahead, a group of platforms will be rising and falling. Between them, a Koopa Troopa and some Brick Blocks, with the final Brick Block on the right containing a power-up. The player will reach a Pipe that will lead them to the final area. They can use the platforms to reach a Warp Zone hidden through the roof. From right to left, the first pipe will head to World 2, the second one will lead to World 3, and the third one will lead to World 4. If the player goes through the regular level pipe, they will lead the player to a pipe with a Piranha Plant in an overworld area. There will be a Block half-pyramid that allows the player to jump on the top of the Flagpole.

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 at the very end of the underground area above the exit pipe, and the score to beat is 38000. The Red Coin locations are: The Warp Zone area at the end has also been changed, containing several Brick Blocks, a trio of ? Blocks, several coins, and a power-up in a Brick Block before the pipe leading to the flag.
 * In the last block to the right in the row of ? Blocks at the start
 * With the other coins above the Brick Block formation near the start of the level
 * On top of the large pillar of Brick Blocks with the hidden 10-Coin Block, just after the second power-up
 * In the 10-Coin block in the secret area through the Warp Pipe, which the player needs to collect all the coins from in order for the Red Coin to appear.
 * Directly above the stone stairs before the downward-moving lifts

Enemies

 * Goombas
 * Koopa Troopas
 * Piranha Plants

Level statistics

 * Power-ups: 4 (Three Super Mushrooms or Fire Flowers and one Super Star), 5 in the Super Mario Bros. Deluxe challenge, with the Warp Zone area containing another Super Mushroom/Fire Flower
 * 1-Up Mushrooms: 1
 * Secret areas: 2

Trivia

 * Like the previous level, this level has also been recreated in various games, including Super Mario Advance 4: Super Mario Bros. 3 (as a World-e level), New Super Mario Bros. 2 (within the first course of the Gold Classics Pack), Super Paper Mario (as part of Chapter 3-1), and Super Smash Bros. Brawl (as an alternate version of Mushroomy Kingdom; there is a chance this stage will be played instead of World 1-1).
 * In Mario Kart 8 and Mario Kart 8 Deluxe, there is on the wall in Super Bell Subway that references World 1-2.

Mondo 1-2 (Super Mario Bros.)