This is a page on planned but cancelled elements in Super Smash Bros. U and 3D. For the actual game, click here.
Double Characters, such as the Ice Climbers and Duck Hunt were at one point considered. However, once again the Ice Climbers were difficult to implement on the 3DS. However, Plusle and Minun, Wario and Waluigi, and something labeled "k.didy.dxie.png", which is most likely Diddy Kong and Dixie Kong, were found in the game's code. And the Duck Hunt Dog is an assist trophy.
Mii Fighters were found in the game's code under the label "mii.cuustom.avatar.png". However, to maintain the same playable roster only with playable and cut characters from SSB64, they were ultimately cut.
Pokè Balls were planned to be items in SSBU+3D. However, a bug kept this from happening. The Poke Balls and Pokemon appear invisible on the stage.
All Star mode was at one point considered in development. However, once again, it was cut to maintain balance between SSB and SSBU+3D.
Sakurai was asked if Smash Run would be returning in the remake. He replied, "No, but it will live to fight in the sequal!" It is unknown if he ment the remake of SSBM, or in the upcoming SSB6.
It was leaked on August 18, 2014 that DLC was at one point considered. Some DLC characters were Palutena, Falco, and Lucario. The method was cut for unknown reasons.