On August 18th and 19th, 2014, several weeks before Super Smash Bros. for Nintendo 3DS launched in Japan, one of the most influential leaks in the series occurred. Footage of the gameplay and the roster (including fighters who were not announced by Nintendo at the time) were uploaded to 4chan, and then YouTube. The legitimacy of the leaks were brought into question by fans (such as the consistency of the rosters compared to the one that was shown at E3 that year), with some speculating that the leaks originated from an employee connected to the Entertainment Software Ratings Board (ESRB), leading fans to refer to the leak as the ESRB leak. It was not until Nintendo took down the YouTube videos very shortly after they were uploaded when they were confirmed to be legitimate. Days later, Shulk would be revealed for the game in a Japanese Nintendo Direct, confirming the rest of the game's unannounced roster.

In 2023, it was discovered that the leaker was a child of a Nintendo of America employee. According to a DidYouKnowGaming? video researching the history of various video game leaks, the employee recorded footage of the game in action, which would be sent to the ESRB for review. The child gained access to it and shared the footage with his friends, before spreading out of control. Nintendo of America fired the employee shortly after word got out.

One of the few tracks included from Donkey Kong Country: Tropical Freeze within the soundtrack for both Super Smash Bros. for Wii U and Super Smash Bros. Ultimate is "Swinger Flinger". However, actually listening to the track reveals it to instead be the theme for the Bopopolis stage.

This error is not presented in the Japanese versions of these games, where the "Swinger Flinger" track is properly referred to by its Japanese name equivalent to Bopopolis, ふみふみラビリンス (Fumifumi Rabirinsu), or Stomping Labyrinth. In comparison, the actual Swinger Flinger track and stage in the Japanese version of Tropical Freeze is called バインラビリンス (Bain Rabirinsu), or Vine Labyrinth.