- For the Special Mode, see Super Sudden Death
Sudden Death occurs when a VS. mode match ends in a tie. All players are given 300% damage, as opposed to zero, making them easy to KO; if items are on, then they do not spawn during a Sudden Death, with the exception of the original game.
If no characters are KO'd after roughly twenty seconds, Bob-ombs will begin to fall from the sky; these Bob-ombs, however, immediately explode when they make contact with players or the ground, thereby speeding up a match. If players dawdle, they can get KO'd by these Bob-ombs while an opponent is sent flying away by a screen or star KO, thereby losing the match. The crowd will not make noises during a Sudden Death.
 Conditions to occur
In Time battles, Sudden Death occurs when some characters have the same final score at the end of the match. In Coin Battle, players with the same amount of coins will fight in a Sudden Death battle; the same applies to Bonus, where players with the same final score will square off. Sudden Death almost never occurs in a stock match (barring a timed Stock Match, where Sudden Death will occur if time runs out and multiple players have the same amount of stocks), though it is possible if all characters lose their last life on the same frame. Kirbycide and other Sacrificial KOs can easily create this situation in matches with two players remaining, and having all characters on a horizontal platform that hits the bottom blast line can also cause it with any number of players.
 Ties in Sudden Death
If all characters are KO'd at the same time in Sudden Death, a second Sudden Death will not be performed; rather, the game ends. The player who wins is chosen via different methods. In the original game, the winner would be the character with the highest player number, while in Melee, the player with the lowest player number will win in the case of ties; for instance, if Player 1 and Player 2 tie in Sudden Death, then Player 1 will win in Melee, yet Player 2 would win in SSB64. As both players must be KO'd on the same frame, and the games run at 60 frames, then the chances of this occurring are slim, and any advantage given to lower player numbers is decidedly negligible. Tests in Brawl Sudden Death mode have shown that the player who wins the match is decided at random.
 In Competitive play
In tournaments, should Sudden Death occur, it is ignored, with the winner being decided by other factors. Sudden Death is not played out in tournaments because of its numerous gameplay issues, while severely skewing matchup balance, as it provides extreme advantages and disadvantages to certain characters. One such issue is in the fact that there is no time limit, and the safest, most effective strategy to win is via using camping tactics to avoid the falling Bob-Ombs, most notably by planking (where the player is essentially immune to falling Bob-Ombs). This gives an extreme advantage to those with strong planking capabilities, while greatly hindering those who aren't that capable at planking. Because of planking being the prominent tactic and there being no time limit, a Sudden Death between two competent players playing to win can feasibly go on forever, often with little to no actual combat between them (as approaching the opponent is extremely risky in Sudden Death, especially if they're planking). In other cases, matches may not last any significant time; faster characters such as Fox and characters with fast projectiles that have some knockback scaling, such as Pit, have a large disproportional advantage, as they can land a KOing blow quickly and relatively safely, while having some of their primary weaknesses in standard play nullified (being lighter or having subpar KO power makes little difference when one hit can decide the match). Additionally, slower and heavier characters are put at a large disproportional disadvantage, as besides typically being less effective at planking, they have some of their primary advantages under standard gameplay nullified (greater endurance and KO power cannot make up for being easier to hit and having harder to land attacks, while under one hit KO conditions). This results in some characters, such as Bowser and Ganondorf, having almost no feasible chance of winning a Sudden Death at a high level of play, while many others see near unwinnable conditions against the favored characters of Sudden Death.
In addition to these gameplay flaws, smashers generally agree that Sudden Death can become an unfair way to stage a comeback. In this regard, Sudden Death can allow a player who was clearly losing before time ran out, such as by having a considerably higher damage percentage than their opponent, to try and equalize by forcing a Sudden Death; the losing player can camp until time runs out, then potentially win the match just by being able to land the first blow in Sudden Death, or by simply camping again. As such, a player that reasonably should have lost if the match had no time limit and continued as normal, won the match despite being outplayed by their opponent.
As a result of being too imbalanced to be used to resolve ties, tournaments instead declare the winner through other ways in the event of Sudden Death occurring; should the usual tie occur with time running out and stock being equal between combatants, the player with the lower damage percentage wins. In the rare event of equal stock and percentage, or with both players being KO'd at the same time on their last stock, a one stock rematch with the same characters and on the same stage is held to determine the winner. If both players are KO'd at the same time due to a sacrificial KO, tournaments often have a rule that declare the initiator the winner, instead of holding a one stock rematch.