After news that new modes would be added to Super Smash Bros. Ultimate in its version 3.0, scheduled for release this April, many fans were eager for announcements in Nintendo Directs and any other news during the month.
Apparently, however, Nintendo did not need any formal announcement to leak a new mode in a commercial for the game.
Didn't see it? Right at the beginning of the trailer, a menu icon appears to indicate the return of Stage Builder!
The game mode, which first appeared in Super Smash Bros. Brawl, allows players to build their own arenas, customizing stages and music. In Super Smash Bros. for Wii U, the mode went further because the Wii U GamePad's touchscreen could be used to build more complex shapes.

This would not be the first time Nintendo unintentionally leaked something from the Smash Bros. series. In a trailer for Super Smash Bros. for 3DS, the character Ganondorf could be seen before an official announcement.
More recently, on the day before Simon and Richter Belmont were announced, Nintendo mistakenly included the title “Bloody Tears/Monster Dance” in the name of a song shared on the game's blog. The Castlevania franchise had not been represented in the series until then.

Ganondorf could be seen as an icon in this small part of the trailer
The funniest part of the whole story is that this time Best Buy was not to blame, even though it had already caused two leaks in the previous month.
Now that Stage Builder is essentially confirmed, what other new features do you expect in the update?