World C is the fourth secret world that was first featured in the game Super Mario Bros.: The Lost Levels, following World B. After clearing this world, the player will gain access to the final world in the game, which is World D.
This nighttime overworld level (which is snowy in All-Stars) mostly has Piranha Plants and Green Paratroopas. There's a warp pipe that leads to a staircase made of blocks with coins. There are also two Poison Mushrooms on this stage so Mario and Luigi need to watch out.
This stage mostly contains bridges and mushrooms-like platforms. There are dangers from above and below with jumping Cheep Cheeps, Bloopers, and off-screen Bullet Bills. This stage has only one ? Block and no Brick Blocks or Warp Pipes.
This stage has treetop-like platforms and springs, and is identical to World 7-3, aside from the fact that this level has Lakitu in it and 7-3 doesn't. The only enemies here are Lakitu (with Spinies) and both red and green Koopa Paratroopas. There is also a strong wind in this stage that blows against the player. This wind can blow the player right off the stage. The player must advance through this level by jumping on green springs that can bounce Mario over pits that are not possible to jump over.
Glitch: The player MUST kill Lakitu before jumping on the fourth spring of the level because if she/he does not do this, the next spring will not spawn, making the level impossible to complete.
This level is exactly the same as World 7-4, except for that a few more Fire Bars have been added. The Koopa Troopas and Buzzy Beetles also move at a faster speed in All-Stars. Another change is the addition of some blocks that appear near two sets of clockwise-moving Fire Bars. The blocks are obviously there to make it harder for Mario or Luigi to get past the Fire Bars unscathed. In fact, there's one area where it's impossible to do so, although there's a hidden Mushroom before it. The fireball-spitting Bowser Impostor is really a Buzzy Beetle in the original FCD version, but in All-Stars, it's a Bullet Bill who throws hammers. After clearing this level, the player must head to the next (and final) secret world.