Super Smash Bros. 4
Two games in the Super Smash Bros. series, collectively referred to as Super Smash Bros. 4, Smash 4, or SSB4 and individually entitled Super Smash Bros. for Nintendo 3DS and Super Smash Bros. for Wii U, are currently in development for the Nintendo 3DS and Wii U respectively by Namco Bandai and Sora Ltd. The 3DS version is the first game of the series to be released on a handheld.
When originally announced in passing at E3 2011, the game's development was slated to begin sometime after October 2011, once development on Kid Icarus: Uprising had completed.  In February 2012, it was then confirmed that development on the fourth game had begun. The game was unmentioned during E3 2012, something which many fans were disappointed about despite the known extremely early state of the game; the "first step of the process" was taken shortly after in mid-June. Masahiro Sakurai has expressed disappointment that fans will be waiting for longer than expected for the game to be released due to the earliness of the initial announcement. Shortly afterward, it was revealed during a Nintendo Direct that Namco Bandai was the primary developer alongside Sora Ltd., and had already completed a working prototype.
The paired versions of the game were officially revealed at E3 2013 in the form of a trailer on June 11, 2013.
According to Masahiro Sakurai, the 3DS version is scheduled to launch this upcoming summer, and the Wii U version this upcoming winter.
Sakurai has stated, in response to a fan asking him about whether a "child Link" would appear in the game, that he had not at the time decided on who would appear in the game. However, he had also said that he "can't say that it's entirely out of the realm of possibility that some Capcom character could appear in the next Smash Bros." Indeed, Capcom's Mega Man was ultimately confirmed as playable.
Sakurai has revealed that one feature of the 3DS Smash Bros. title will be that players can improve their character through battles and rewards, then transfer them to the Wii U Smash title to play against friends. He said the 3DS title is intended to offer a new experience for veteran Smash Bros. fans, and that neither the 3DS game nor the Wii U game would simply be sequels like Melee and Brawl were, and that they'd do more than just add characters and stages. It has also been revealed that they are looking towards co-operative play for the Wii U title. Official Nintendo Magazine said "there is merit in having skilled and unskilled players play together, so one emphasis will be on elements of players helping one-another". They also stated that the graphics would be significantly stepped up, as the Wii U can handle high quality graphics, dynamic effects and smooth character movements in HD at 60 frames per second. Sakurai is also quoted as claiming that the new game is unlikely to emphasize new playable characters, focusing instead on gameplay balance and distinctiveness of its characters. 
On July 2nd, 2012, Sakurai posted a whiteboard drawing on Twitter which was drawn by the game's staff. It depicts Donkey Kong, Fox, a Heart Container, Kirby, Link, Luigi, Mario, Marth, Meta Knight, Mr. Game & Watch, a Mr. Saturn, Pikachu, a Pikmin, Pit, Sandbag, Wario, and Zero Suit Samus; some argue that the curved lines in the background form the shape of Master Hand. While it came with no explicit confirmation of any of these characters or elements as reappearing, it does show they are in some sense acknowledged by the staff working on the game. The image itself was later removed from the original Twitter post. The sketch also has what appears to be large block letters hidden below the visible area.
The trailer shown at the E3 2013 Nintendo Direct confirmed several characters, both returning characters and new characters. Since that time, other characters have been revealed on the website, sometimes at the same time as Nintendo Directs.
In the beginning Sakurai had made it clear that there would be a single-player story mode included in the new Smash Bros., however stated it would be different from Brawl's Subspace Emissary, and there would be no cutscenes. He did not provide any other details as to what this, or any other single-player modes will consist of. On 20 January 2014, on a Miiverse post, Sakurai repeated his very first statement of the game not featuring a Subspace Emissary-like Story Mode. Screenshots that were seemingly implied to be from a new story mode in the 3DS version were later revealed to be from Smash Run.
Outside of what little info is available on Smash Run, details about the games' other single-player modes are still unknown at this time.
Apparent changes from Brawl
Other apparent changes
The Wii U and 3DS versions of the game were shown to have distinct art styles from one another in that the 3DS version uses flatter shading and optional black outlines to make characters easier to see at a distance; these outlines will be customizable as Sakurai stated players can change the size of the outlines or get rid of them completely. It is also known that several if not most stages will be version-specific, with the Wii U version's stages being based on console games, while the 3DS version's stages being based on handheld games. It is confirmed that there will be no cross-platform gameplay between the Wii U and 3DS versions due to the exclusive stages to each version, but it has been mentioned that "customized characters" from the 3DS version can be imported into the Wii U version. Very little detail has been given as to what "character customization" entails; it has only been revealed that customizations will not be different costumes and will not have to be unlocked through repetitive tasks.
While the two versions will have the same playable cast, it has been confirmed by Sakurai that there will be a few differences with the characters summoned from Assist Trophies and Pokemon summoned from Pokeballs in the 3DS version, though it has not been stated if there will either be explicit version exclusives or a few will be cut out of the 3DS version for space issues.
Another difference confirmed by Sakurai is that the trophies will be different in the two versions, with the trophies in the 3DS version being mainly from handheld games, while the trophies in the Wii U version will be from console games.
When it comes to music, each stage on the 3DS version will only have two music tracks available, as was the case in Melee; this is presumably because of space issues on the 3DS cart. On the other hand, the Wii U version will see the return of Brawl’s My Music option, with a large selection of tracks available for each stage.
Sakurai has stated that there are currently no plans to implement downloadable content or touch screen controls of any variety.