World B is the third secret world that was first featured in the game Super Mario Bros.: The Lost Levels, following World A. If the player completes this world, the player will gain access to go to World C.
This level is an underwater level which has several features including a long Fire Bar near the end.
This level has very long pits which require the use of several platforms to be cleared.
This level is a castle level which has a few lava pools in it. The second, third, and fourth pipes all go back to the first pipe (all the pipes contain red Piranha Plants). The last pipe leads to a Warp Zone to World D. At the end will be the Bowser Impostor, the axe, and the Toad, before advancing to World C.