Super Smash Bros. Ultimate is a fighting game for up to eight players in which characters from Nintendo games and from other third-party franchises must try to knock each other out of an arena. Each player has a percentage meter which raises when they take damage, making them easier to launch in the air and out of the arena. Standard battles use one of three victory conditions: Timed, where players aim to win the most points by defeating opponents within a time limit, Stock, where players have a set number of lives and must aim to be the last player standing, and Stamina, where players must simply reduce their opponent’s health down to zero to defeat them. Players can adjust the rules to their liking and save them as presets for future matches.

Players can use various items to attack enemies or grant them power-ups, along with Poké Balls and Assist Trophies which respectively summon Pokémon and other non-playable characters to assist them in battle. In Timed matches, certain Assist Trophies can be attacked and defeated to earn points. Each character also possesses a powerful Final Smash attack, which can be performed either by obtaining a Smash Ball item or by filling up a special meter, both of which can be toggled on and off. The game features 103 different stages included in the base game, with additional ones coming packaged with DLC fighters. They can all be played in alternative Battlefield and Omega forms or can be toggled to remove stage hazards. A new feature called Stage Morph allows players to select two stages that the game alternates between at certain intervals during a match. Other tweaks include new icons and gauges for character-specific abilities, such as Cloud’s Limit gauge.

In addition to returning modes such as Classic and Special Smash, new modes added to the game include Smashdown, where each character can only be played once, Squad Strike, where players battle in teams of multiple characters, and Tournament, which allows up to 32 players to battle in tournament brackets.