World 9 (New Super Mario Bros. Wii)

World 9 is a bonus world from New Super Mario Bros. Wii, unlocked by defeating the final boss of World 8. Each of the eight levels in this world are unlocked by getting all of the Star Coins in the world of the corresponding level number (e.g. All Star Coins in World 1 unlocks World 9-1). World 9 also has Star Coins, but the player doesn't unlock any new stages for collecting them all. There is a total of 24 Star Coins in World 9. Regardless, they're still needed if the player wants to get all five stars on his/her profile on the file select screen. Despite being a rainbow-themed world, the levels take place in places other than rainbow-themed ones.

World 9-1
Although this stage is unlocked for World 1, the layout is similar to 7-1. There are lots of spinning rectangle platforms around the level. Also appearing is a big L shaped (also spinning) platform. Like all World 9 levels, there is no halfway line, making it difficult to traverse the level. Koopa Paratroopas are the main enemy in this stage.

World 9-2
This stage takes place at a beach setting. The player must get to the goal avoiding a Porcu-Puffer and many Koopas. In this level there are lots of spots were players can fall. Cheep-Chomp makes its main appearance in this level.

World 9-3
This course has the background of World 6. It features Missile Bills and Missile Banzai Bills. POW Blocks cannot defeat these enemies. The floor resembles that of World 7-2.

World 9-4
World 9-4 involves a desert landscape, which has many pipes and auto-scrolls. Most of its enemies are Venus Fire Traps and Bob-ombs. Its main power-up is an Ice Flower, which is required to get the last Star Coin.

World 9-5
A snow level where the player must get to the top of the Icy Mountain, while avoiding Cooligans, Fuzzies, and Mega Fuzzies. The first Star Coin is just outside a pipe that spawns Cooligans, and can be easily obtained by sliding with the Penguin Suit. The second one is near another pipe, and can be obtained with a wall jump, though sliding is still recommended. The last one is tricky, as the player must freeze a Fuzzy to use it as a platform to reach it.

World 9-6
A lava level, where platforms emerge and descend into the lava. The only enemies in the entire level are Fire Chomps, which can make the level a bit more difficult.

World 9-7
The penultimate course is notoriously difficult. The level takes place in a snowy forest, with floors made of ice blocks, and pipes. Venus Fire Traps, Piranha Plants, and Fire Bros. appear in this level, using their fiery attacks to burn open chestnut shells, revealing Goombas, and melting away the frozen landscape, making it difficult to traverse. Munchers also make an appearance in this level.

The first Star Coin is found near the beginning, between some Venus Fire Trap pipes. The second one requires the use of Fire Mario or Venus Fire Traps to melt the ice blocks covering the star coin. The last one can be obtained by letting the Fire Bros. use their own fire balls to melt the ice and wall-jumping, or using Propeller Mario.

World 9-8
The last stage of the game is a sky level. In it, the "floor" is made of several clouds that let Mario jump every time he falls on them. A little ahead, two ? Blocks are found and one of those contains a Propeller Mushroom, which can improve a player's chance of survival greatly. A little more forward, the first Star Coin is found surrounded by Fuzzies and after this part, a Random Item Block is found surrounded by 5 Fuzzies, one being a mega. Below them, a ? Block from the right contains a Mini Mushroom that can help the player to access high places. After that, the second Star Coin is found alongside Fuzzies.

Forward, King Bills begin to break down walls so Mario can continue his progress. The third Star Coin is found stuck between walls that a King Bill will destroy. Arriving at the end of stage, a last King Bill will appear near the flagpole where it can be destroyed if the player jumps on the flagpole before being hit by it. This course has the background from World 7.

Enemies Introduced

 * Missile Bills
 * Missile Banzai Bills
 * Munchers
 * King Bills

Trivia

 * This world is similar to the Special World and Star World in Super Mario World, and to the Rainbow Road from the Mario Kart series.
 * The Rainbow Road theme from Mario Kart 64 can be heard at some point in the World 9 map theme.
 * None of the levels have Half Way Flags.
 * World 9-8 has rainbow platforms that bear a slight resemblance to the world itself.