The game follows the series' traditional style of gameplay, in which players control one of the various characters and use attacks to weaken their opponents and knock them out of an arena.

Sakurai's goal with Ultimate was to include every character from previous games in the series, despite the various development and licensing challenges this would present.

Several well-known video game musicians contributed to the soundtrack, with Hideki Sakamoto writing the main theme "Lifelight".

Ultimate is a platform fighter for up to eight players in which characters from Nintendo games and third-party franchises fight to knock each other out of an arena.

Each player has a percentage meter which raises as they take damage, thus increasing the knockback they take and making them easier to launch in the air and out of the arena.

For example, the Spirit battle of Rayquaza, a flying dragon Pokémon, requires players to defeat a large version of Ridley with a similar color palette and wind effects.

[12][15] The mode's narrative begins with an evil entity, Galeem, destroying the Smash Bros. world, vaporizing almost all of the fighter characters and placing them under his imprisonment; only Kirby, due to his Warp Star, evades this attack.

Ultimate, like other games in the Super Smash Bros. series, features a crossover cast of fighters from several different Nintendo franchises, as well as fighters from series by third-party developers such as Konami, Sega, Capcom, Bandai Namco Entertainment, Square Enix, PlatinumGames, Atlus, Microsoft, SNK, and Disney.

The first of these, Piranha Plant from the Mario series, was released in January 2019 and made available for free to those who purchased and registered the game with a My Nintendo account before the end of that month.

[31] Unlike previous Super Smash Bros. games, the team was not assembled from the ground up, which sped up preparation time.

[51] Sakurai also wanted to adjust character abilities to speed up the game,[31] although not to an extent that would alienate players unfamiliar with the series.

[52] Sakurai knew that Ultimate was a core game for Nintendo and that it had a dedicated player base that he did not want to disappoint, and believed that completing this goal was necessary to satisfy them.

[61] The addition of Ridley from Metroid as a playable character had been highly requested within the Super Smash Bros. community for some time.

[54] All characters were chosen at the beginning of development except for Incineroar, who had not been created yet;[63] the team instead left a space open for a Sun and Moon Pokémon.

[6] The World of Light mode was inspired by Brawl's (2008) Subspace Emissary, and Sakurai chose to start it with a cataclysmic event because he thought it would leave a greater impact on players.

[64][65][66] New to Ultimate is the tying of tracks to franchises instead of individual stages, as well as the ability to create custom playlists to listen to outside the game when the Switch is in handheld mode.

[64] Sakurai stated that he began contacting composers over a year before release, providing them with a database of over a thousand suggested track ideas.

[67] While Sakurai oversaw the process and preferred that the music retain the spirit of the original games, the direction of them was generally handled by the composers themselves.

[73] Sakurai noted that Banjo and Kazooie were the second most requested character for Super Smash Bros. for Nintendo 3DS and Wii U in a Nintendo-sanctioned fan vote in 2015,[74] and that their addition happened "quite easily", despite the property being owned by Microsoft through its acquisition of Rare.

[75] Phil Spencer, the head of Xbox, stated that negotiating their inclusion was "an easy deal to make" thanks to Microsoft's strong partnership with Nintendo.

[43] According to Daniel Kaplan of Mojang Studios, early discussions between Nintendo and Microsoft about including Minecraft content in the Super Smash Bros. series had begun roughly five years prior to Steve's addition into the game.

[77] The character's inclusion required the development team to rework every stage in the game to accommodate Steve's gameplay mechanics.

[78] Sakurai had wanted to include Sora from Kingdom Hearts in the game because he was the top fighter requested for Nintendo 3DS and Wii U in the 2015 fan vote.

[79] However, they initially thought that the legality surrounding the intellectual property with Disney would be insurmountable, and originally planned for only five fighters in the second pass.

Nintendo, Disney, and Square Enix saw towards including Sora in the game and overseeing all aspects related to his inclusion, with several limitations and guidelines they were required to follow.

[81] Ultimate was teased during a Nintendo Direct presentation on March 8, 2018, under the working title Super Smash Bros., with the release year shown to be 2018.

Some users on social media saw this as racist, leading to Nintendo of America apologizing and removing the animation in an update shortly after release.

Nintendo took steps to issue copyright strikes on YouTube videos using data mined content, while fans worked to isolate spoilers, particularly the World of Light story mode, from those that had played the leaked version.

[119] Within 11 days of its release, Ultimate had sold more than three million copies within the United States, making it the fastest-selling Switch game in the country.

[148] On May 8–10, 2020, top Super Smash Bros. Melee player Hungrybox partnered with NFL running back Le'Veon Bell and esports organization Team Liquid to host The Box, an online tournament with a $10,000 prize pool.