This is a list of beta elements and unused content in New Super Mario Bros. DX. According to some of the developers of the game, some of these elements will be reworked and used in the upcoming sequel of the game, Newer Super Mario Bros. DX. The elements that will be used haven't been specified as of yet.
- Wario is originally going to be a playable character in the game. He would retain his abilities and gameplay from the Wario Land series. He was even mentioned durnig interviews and trailers, but in the trailers Wario was only shown in 1 player - This is because of a huge bug in the game. The developers had no trouble putting his gameplay in single player mode; It was when they starting putting it in multiplayer when they started having trouble. When Wario and another character played a level in multiplayer, sometimes the game would accidentally give Wario the normal gameplay and the other player Wario's gameplay. Since the developers couldn't find out how to remove the bug, he was cut from the game. Code for his gameplay still exist within the game and so is his model.
- In an interview with Mr. Iwata, he revealed that Waluigi was also going to be playable, and both he and Wario were going to have a major role in the story as well as their own unique gameplay styles. Waluigi was never shown in trailers, and none of his models or coding exist, so what his gameplay would be like is unknown.
- The Superball Flower and the Carrot from Super Mario Land 1 and 2 were both originally power-ups. They would act similarly to their Gameboy counterparts, but 2 superballs could be thrown at once, like the Fire Flower and Ice Flower. They were both shown in screenshots but were never seen in trailers, because the screenshots were taken and shown early in developement and were scrapped before the first trailer was created
- The Burning Mushroom was going to make an appearance. In this game, it would be an enhanced version of the Fire Flower. A Burning Meter would appear at the bottom left after being used, and would slowly increase the more Mario ran, like Raccoon/Tanooki Mario's P-Meter. When the meter was filled, Mario would go so fast he'd turn into a giant, unstoppable fireball, and could destroy almost anything in his path (including stairs made of tiles, enemies, blocks, and even the Goal Pole!) for a limited time. During the fireball state the Burning Meter would slowly decrease, and when it went out completely Burning Mario would go back to normal.
- For some unknown reason, the Mario Head clips from Mario Teaches Typing 2 are in the game's files in the same directory as the cutscenes, but they're changed in a few ways. For example, in the clip where Mario sings a song, when he says "When an eel lunges out", a picture of Unagi from Super Mario 64 is seen for a split second before going back to Mario.
- Some unused levels have been found and can be played using Action Replay codes. Most of them are either test levels (used to test certain things like powerups and character physics) or unfinished versions of existing levels. However there is a rather interesting level that is a recreation or World 1-1 in New Super Mario Bros. DS. This has given people the theory that the game was originally going to have recreations of levels from New Super Mario Bros. DS, perhaps as DLC or by beating the game.
- There are a few unused models in the game, as well as some placeholders. For example, there's a Yoshi Egg that can be picked up and thrown, but Yoshi never comes out. There are also models from New Super Mario Bros. U, since the game was made on a modified New Super Mario Bros. U engine. Other models include a Cosmic Clone, a beta version of Cape Mario, a giant Bob-Omb, and a working Gooper Blooper boss battle.