According to Masahiro Sakurai, Bowser Jr. was very close to not being included in the game's roster.

In international releases of the game, the Porky Minch trophy's game chronology only mentions his appearance in EarthBound and not Mother 3, even though the trophy description mentions both games and the trophy's design is taken from Mother 3.

Bowser is the only veteran in the game to not have his victory theme ripped straight from Super Smash Bros. Brawl.

Jigglypuff's character model in the 3DS version is recycled from the model used for Jigglypuff in Pokemon X & Y.

Chrom was originally intended to be a playable character in the game, but was replaced with Robin as Sakurai thought he'd play too similar to Marth and Ike, and that Robin would be a more unique character. Chrom still however appeared as a part of Robin's Final Smash, and did become playable in the next game in the franchise, Ultimate

During the song "Master Core" (which plays when fighting the identically-named boss in Classic Mode), the instruments will silence after 1 minute and 53 seconds and a series of beeps will play for six seconds before the instruments start playing again. These beeps are Morse Code for "MASTER CORE".

If Shulk is on the Gaur Plains stage when Metal Face appears, Metal Face will occasionally say unique taunts.

The taunts are:
• "If it isn't the puny boy himself.You miss me?"
• "Hey, Monado boy, I don't think you can hurt me with that thing"
• "OH! It looks like Monado boy's been practicing"
• "If the brat's here, I bet Dunban can't be far behind."

The amiibo figures sold alongside the game are well known for having a number of defect units. These include, but are likely not limited to:
• Samus having 2 cannons instead of 1.
• Marth having 2 swords instead of 1.
• Peach having no legs.
• Luigi missing his left hand.

When Pit gets KO'd he'll sometimes say, "I'm Finished". This is a reference to the original Kid Icarus Game Over screen.

The trophy for the Lurchthorn enemy from Kid Icarus: Uprising references Superman. The first sentence reads, "Is it a bird? Is it a plane? No, it's... some kind of giant fossilized fish."

While Xander Mobus, the game's announcer, recorded a shout of the game's name (much like Super Smash Bros. Melee), it went entirely unused in the final game's release.

Unlike all previous entries in the Smash Bros. series, Jigglypuff uses the standard Pokémon palette as apposed to her shiny palette. This is most noticeable in her eye color.

The description for the "Souflee" trophy from Kid Icarus reads, "We could tell you it's a cake, but that would be a lie". This is a reference to running gag through the first Portal game, stating that "the cake is a lie".

Lucina is the only unlockable character who was officially revealed prior to the game's 3DS release and is the first female unlockable character in the Super Smash Bros. series.

Originally, Flying Man had both a 2D and 3D model for when he appears on the Magicant stage. The 3D model was scrapped however, to lessen strain on the 3DS hardware.

As of Super Smash Bros. Ultimate in 2018, only three characters that started out as Assist Trophies became playable in future installments:

•Little Mac, an Assist Trophy in Brawl, then became playable in Super Smash Bros. for 3DS/Wii U
•Dark Samus, an Assist Trophy in Super Smash Bros. for 3DS/Wii U, then became playable in Ultimate
•Isabelle, an Assist Trophy in Super Smash Bros. for 3DS/Wii U, then became playable in Ultimate.