Quickplay has two game modes: Co-op and Solo. Co-op allows two players on the same console to play online doubles against other players on the same console. Solo allows players to play in 1v1 matches against other players with similar GSP (Global Smash Power) and region. When one of the player's characters reach a certain GSP Global Smash Power, Solo mode becomes Elite Smash, but only for that character. If all the characters lost the Global Smash Power to qualify for Elite Smash, the mode returns to normal Quickplay. The higher every one of someone's characters' Global Smash Power, the higher the player's roster GSP will be, which increases the amount of Global Smash Power a character they haven't played yet will start out with. This system makes it easier for people who already have characters in Elite Smash to get more in.
If the network connection is unstable, a message will pop up and not allow quickplays. If a player disconnects during a match, their GSP will be lowered and they will receive a warning when they reopen the game. On the opponent's side when a player disconnects, the game will freeze and a loading icon will appear for a few seconds, the disconnected player will be replaced with a CPU and they will receive no GSP when the game ends, regardless of whether or not they beat the CPU. If they keep disconnecting, they will get a temporary ban from Online Tournaments, Battle Arenas, and Quickplay that gets longer the more times a player disconnects. Contrary to popular belief, players do lose GSP if they disconnect at the end of a match. They will receive the previously mentioned punishments, but their opponent will not gain GSP. A player's account will be temporarily banned or punished if they disconnect mid-match, if they are inactive, if they target one player in a free-for-all, if they excessively self-destruct, if they stand in place and only use one move, and other behaviors.
Unlike its predecessor, Solo mode does not include For Fun or For Glory. Instead, players can set a preferred ruleset before selecting a mode. This ruleset allows users to have a higher chance of fighting opponents who have a similar ruleset, although it's not guaranteed. When preferred rules are turned off, it allows any other players to decide how a match is played. During the game's launch, there were many complaints from players because they were not entering matches with the ruleset they wanted; however, the game has since been updated to more commonly place players in 1v1 matches if they set 1v1 as their preferred rules.
Preferred rules include the following:
- Three formats are available: Smash (Free-For-All), Team Battle, or 1-on-1.
- Three rules are available: Time, Stock, and Stamina.
- Time allows for matches with the times 2:00, 2:30, and 3:00.
- Stock allows for matches lasting 3:00, 4:00, 5:00, 6:00 or 7:00, with 1, 2 or 3 stocks.
- Stamina allows for Stock matches with each stock having 100, 150, 200, 250, or 300 HP.
- Five stage options are available: A random stage, a random stage with hazards off, a random Battlefield form, a random Ω form, and Small Battlefield (since update 8.1.0).
- Since update 3.1.0, FS Meter can be toggled.
- The following five item groups can be toggled on/off: Smash Balls, Assist Trophies, Poké Balls/Master Balls, Dragoon/Daybreak pieces, and all other items. Prior to update 3.1.0, Special Flags were another item group.
Unlike other modes in Ultimate, it is impossible to taunt in Quickplay, including the characters that have their taunt as an attack (i.e. Luigi and Kazuya). The only exception to this is Kirby, who can taunt when he has a Copy Ability in order to discard it. This restriction is likely present in order to prevent taunt matches (even though taunt matches do not necessarily require taunting) and mitigate potential toxic player behavior taunting enables.