World 6- is the castle level and final level in World 6 of New Super Mario Bros. 2. It is unlocked after completing World 6-5. In the Coin Rush game mode, this course is never selected, likely due to the length of the Bowser battle.
This level is similar to World 8- in New Super Mario Bros. Wii. In the first section of the level, there are Burners on the rope moving near the lava, and Podoboos and Dry Bones can be found. The Burners will start turning on and off near the middle of the first section. Near the stages going up, on the very right, there will be a Brick Block which will turn into a Gold Block. In the second section, Mario/Luigi must ride on the Snake Block. Before the blocks pass the platform with the Star Coin, the player must jump down to the platform to reach the Star Coin. The player must then avoid the Burners while the Snake Blocks reach the platform on the door that leads to the third section. Using the Super Leaf, the player can fly to the left and approach an area with a Dry Bones, two blocks that contain coins, and a Hidden Block that contains a 1-Up Mushroom.
Once the player enters the third section, the Koopalings will ride on the Koopa Clown Car and try to turn the player into stone. In order for the player to dodge, they must go behind the walls although the platforms are moving. If the player is shot, they will temporarily turn to stone, immobilizing them for a few seconds, and consequently costing them a life if the moving platforms deposit them into lava. Near the middle of the section, there will be sets of Donut Blocks. On the first set in the middle row, the player must ride down the Donut Block to get the Star Coin. After getting the Star Coin, the player must jump on another Donut Block or the platform in order to stay alive. The player then enters the room to the final battle.
The path to the final battle starts similar to the one in World 8-Bowser's Castle from New Super Mario Bros. Wii. The player gets a checkpoint right after the gate and gets three Item Blocks containing two Fire Flowers and a Super Leaf. After the player gets the power-ups, they must go up the steps and dodge the fireballs that Bowser spews before finally facing him.
Like most of the previous games, Mario must get past Bowser and press the ! Switch to knock him into the lava. After defeating Bowser, however, Peach's cage is yanked off-screen, and Mario must ride a series of platforms upward to another room. Here, the Koopalings use the collective power of their wands to revive Bowser into the enormous Super Bowser; he then stands up knocking them away, and roars, signaling the start of the true final battle. Mario must now climb up a series of rising platforms that fall when he touches them while avoiding the lava below him and dodging Super Bowser's claws and occasional flame attacks. Upon reaching the giant ! switch at the top and pressing it, the floor collapses under Super Bowser, causing him to fall and defeating him once more. Mario then finally frees the princess and escapes the castle.
Later on, the Koopalings attempt to carry Bowser away in the Koopa Clown Car, but Bowser weighs them down and causes the vehicle to crash.
- Star Coin 1: The player must jump straight up while on top of the third Burner to reveal a Hidden Block with a 1-Up Mushroom in it. The player then must climb that block to reach a secret area with the first star coin.
- Star Coin 2: In the second section of the level right after Mario go on the Snake Blocks, near the Item Block, jump down to the platform to reach the Star Coin before the Snake Blocks pass the platform.
- Star Coin 3: In the third section on the first set of Donut Blocks in the middle, the player must ride down one of the two middle Donut Blocks to get the coin. Immediately after getting the coin, the player must jump off the Donut Block and go to another one.