According to Masahiro Sakurai, the reason the Ice Climbers were cut from the roster is because of 3DS hardware limitations. He also states that he didn't want to add them exclusively to the Wii U roster to avoid there being considerable differences between the two versions.

According to series director Masahiro Sakurai, Dr. Mario, Dark Pit and Lucina were originally considered to be alternate costumes for Mario, Pit and Marth respectively, but were eventually changed to be their own separate characters with slight differences in their movesets from the three.

All of the characters in the game were chosen at the start of development. This means Geninja was chosen before Pokemon X & Y was released, and that its inclusion was not because of its popularity.

There was an open slot for a new Pokémon character, and the team began discussing who to put in it, eventually settling on Greninja. All the reference material they had for Greninja were simply drawings at that point. Sakurai went home the same day he received the Greninja reference material and stayed up until midnight to do the motion capture for the character.

The Japanese trailer introducing Mega Man in Super Smash Bros. for 3DS and Wii U has "Clash Man" (the original Japanese name) instead of "Crash Man" (the English name) in the Japanese commercial, despite being changed to Crash Man in Japan.

In Melee, Nintendo 3DS & Wii U, and Ultimate, if the game language is switched to Japanese, Mewtwo will speak in full sentences for some of its victory poses. In English, Mewtwo only laughs during its victory poses and taunt.