Sudden Death (サドンデス, Sudden Death) occurs when any VS. mode match ends in a tie. A tie happens when at least two characters or teams have the same final score at the end of a Time match, the same amount of stocks at the end of a timed Stock match, the same amount of coins at the end of a Coin Battle, or the same total score at the end of a Bonus match. In an untimed Stock match, Sudden Death is possible if all remaining characters lose their last stock on the same frame.
In matches with three or more players, Sudden Death will only occur with the players who are tied for first, excluding the other player(s).
When Sudden Death occurs, the words "Sudden Death" will appear on-screen with the announcer calling it, followed by the "GO!" signal, and the match will restart with only the players involved in the tie, all of whom are given one stock and 300% damage, making them very easy to KO in a single hit. In effect, this makes it so the first player to land a hit on their opponent(s) wins Sudden Death and therefore the match. With the exception of the original Super Smash Bros. and certain stages in various games, items will not spawn at this time even if they are turned on.
From Melee to Smash 4, if nobody wins after roughly 20 seconds, Bob-ombs begin to fall from the sky to speed up the match. Unlike the Bob-omb items, these immediately explode on contact with any surface or player. In Melee, the Bob-ombs act a little differently than in other games - they have no animation for appearing and can explode in mid-air without touching anything. As all players have 300% damage, getting hit by a Bob-omb is essentially an instant KO; however, with precise timing, players can grab Bob-ombs in midair with air dodges or tech on any walls. Prior to Smash 4, it is possible for a falling Bob-omb to instantly KO a player by launching them toward a side blast line while the other player is currently being sent flying by a Screen KO or Star KO, causing the latter player to win the match in the middle of their KO animation; in Smash 4, Star and Screen KOs normally no longer occur during Sudden Death.
In Ultimate, the camera will start at a fixed position and gradually zoom in from the center of the stage from the start of Sudden Death, with the blast zone shrinking alongside it until the camera itself is zoomed in very closely. After a few seconds, Bob-ombs will drop down in an attempt to eliminate players lingering in it too long. This is presumably to balance the gameplay speed of Sudden Death across all stages, especially with larger stages (such as Temple, New Pork City, 75m, Palutena's Temple), autoscrolling stages (such as Mushroomy Kingdom and 3D Land), or with Stage Builder stages. The screen also now has flames around it from corner to corner, surrounding the center. If the battle is in Stamina Mode, all players will have 1 HP instead of 300 percent.
Should a tie occur within Sudden Death itself, which can only happen if all remaining characters are KO'd on the same frame, the match will end and a random player is selected to be the winner. In the first two Super Smash Bros. games, placement is based on port priority: in the original Super Smash Bros., the winner is the player with the highest port number (whose controller is closest to P4), while in Melee, the winner is the player with the lowest port number (whose controller is closest to P1). As multiple players must be KO'd on the same frame for this to occur and the games run at 60 frames per second, the chances of this occurring are slim and any advantage given to certain player numbers compared to others is decidedly negligible, especially since Sudden Death is never used in competitive play. In Brawl, tests have shown that the winner of the match is decided at random. In SSB4, the winner is whoever dealt the most damage, with the placement of the other players following suit. The winner is decided at random if all players deal the exact same amount of damage. The same is true for Ultimate, with the addition of a player that was elimated early potentially being randomly selected as the winner in games with more than two players.
In SSB4's Tourney mode, Sudden Death did not occur in Regular Tourneys and could be disabled in player-made Tourneys as well. If a tie occurred when Sudden Death was disabled, victory was awarded to the player who dealt the most damage throughout the match.
In competitive play
If a Sudden Death occurs in a tournament, it is usually ignored and the winner is decided by other factors. Using Sudden Death as a tiebreaker brings with it a number of complications:
Should Sudden Death occur in a tournament, the winner is declared by some other criteria depending on context. In the most common cause of the clock expiring while both players are tied in remaining stocks, the player with the lower damage percentage wins. In the rare event of both players having equal stock and damage, or if both players are simultaneously KO'd (on the same frame) on their last stock, the winner is determined through a one-stock rematch with the same characters on the same stage. However, this is such a rare occurrence that it sometimes never crosses the mind of tournament directors, which leads to panic when there is no rule in place when it inevitably does happen. If both players are KO'd at the same time due to a sacrificial KO via a command grab such as Flying Slam and Flame Choke, tournaments sometimes have a rule that declares the initiator the winner, instead of holding a one-stock rematch, though this ruling is rarely used by any tournaments in the post-Brawl era.