Super Smash Bros. for Wii U will include eight-player battles for the first time in Nintendo's crossover fighting series.
Available only on special stages (so all the fighters will fit), the mode will also be limited to local multiplayer only.
Nintendo revealed the feature in a new 30-minute Nintendo Direct-style broadcast, available to watch in full below.
The other major announcement was the reveal of Pokémon favourite Mewtwo as a returning playable character - via DLC.
Mewtwo is due for release in spring 2015 for both 3DS and Wii U versions of the game, and will be free for anyone who has bought each version and registered them on Club Nintendo.
Anyone who does so before 13th January will also get a two-disc physical CD album of the 3DS and Wii U version's music.
Metroid boss Ridley - another much-requested character - will appear in Smash Bros. for Wii U, albeit as a stage hazard on the Metroid-themed Pyrosphere stage. The player who deals the most damage to him will gain him as an ally, but KO him and it will count as if he were another player.
Challenges, coin battles, stock matches and the usual array of Smash Bros.' ridiculous match rules are all back.
The Angry Birds-style Target Blast mode, Multi-Man mode, Home Run Contest and Trophy Rush are all included.
Classic mode and All-Star modes will also return, and are now playable with a friend.
If that wasn't enough, single-player and co-op Events are back too, with the usual objective-based rules.
You can also challenge yourself with special requests from Master Hand and Crazy Hand. The former focuses on difficult missions, while the latter allows you to continue taking on tasks - rising in difficulty but also reward level - and gamble how long to continue your streak. You'll need to fight Crazy Hand at the end of each run, where losing will mean you leave with nothing.
Want even more? An all-new board game mode, Smash Tour, was also shown. It's a cross between Mario Party and Smash Bros. for 3DS' Smash Run, where you must battle and collect fighters.
Just as in Smash Bros. Brawl, there's a Masterpieces mode with quick demos of old Virtual Console titles - which will now link you to the eShop to download the full version.
And, improved from Brawl, the game's Stage Builder is also back. You can now draw your own levels freely using the GamePad's touchscreen and stylus.
Voice chat before and after fighting online is also possible - but not during battles, to save your internet connection.
Finally, a number of features will be added post-launch. A Tournament mode is in the works, but not yet ready for inclusion. Similarly, the ability to send screenshots, custom stages and replays to your friends will be added in at a later date.
See all of the above in action via Nintendo's feature-stuffed video below.