World 9 has a total of 24 Star Coins, which are needed if the player wants to get all five stars on their profile on the file select screen.

The rainbow theme is similar to the Rainbow Road courses in the Mario Kart series, with the world map music even being an arrangement of Rainbow Road's music from Mario Kart 64. The Super Guide will also not appear in World 9, even if the player dies eight times in the same level. The levels in World 9 are among the most difficult in the game, and none of them have midway points in them, which adds to the world's challenge (like the Special Zone from Super Mario World). Each level features the background and a music track from one of the previous eight worlds. For example, collecting all Star Coins in World 1 will unlock World 9-1. Each of the eight levels in this world is unlocked by collecting all of the Star Coins in the world of the corresponding level number. It is a special world unlocked by defeating Bowser in World 8. World 9 is the final world from New Super Mario Bros.

“Oh, Mario, did I ever tell you about that secret world?” - Princess Peach, New Super Mario Bros.

Super mario bros 3 world 6 level 9