It was never supposed to be Super Mario Bros 2. It was originally called Doki Doki Panic, and it had nothing to do with the famous plumbers from Brooklyn. The reason that Nintendo of America reskinned this game was that the true sequel would turn off players. What eventually was called Super Mario Bros The Lost Levels was the true sequel and it was an experience in madness. It did bring features that would become staples for the Mario universe going forward.
The plot is the same: Princess Toadstool has been kidnapped by Bowser and it is up to Mario and Luigi to save her. Things have changed in the Mushroom Kingdom. It all looks the same, but the skill required has been ramped up. Imagine if you were playing a game and halfway through, the game decided to put the difficulty from easy to insane. It looks the same, but it requires a different approach. Speed run this, I dare you.
The programmer must have had the worst year ever. How else to explain some of the new features of this game. Mushrooms that do not make you grow, but instead hurt or kill you. Wind guests that seem to kick up the second you jump. Warp zones that send you back levels. The most evil thing is the fact that to clear some levels, you have to find and jump on invisible blocks. This is pre-internet kids, no message board is there to help you. If the first game was about running, this was about precision.
The poisonous mushroom found it’s way into other Mario games. The other development was even bigger. There was no two player mode, you picked Mario or Luigi. Luigi was not just a green copy of Mario. Luigi could jump higher and had less traction when he landed. This might be one of the earliest examples of a different character in the same game. Luigi in Mario Bros 2 had the same abilities. Luigi would continue to be different then Mario as the game series progressed.
American gamers finally got to “enjoy” this game when it was released with Super Mario All Stars. It took a little while, but Western audiences got to experience the suffering that the Japanese had been dealing with. If you have a chance, stay as far away from The Lost Levels. It makes those expert levels that people create in Mario Maker seem like a cake walk. Invisible blocks, are you kidding me?