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. This mode can be instantly accessed via the Special Melee or Brawl mode "Super Sudden Death". After a certain amount of time, Bob-ombs will begin to fall from the sky and explode, a feature which is absent from the Special Melee version. This is also present in special Brawl, under the name 300%.
Sudden Death almost never occurs in Stock mode (barring a timed Stock Match), though it is possible if all characters lose their last life at exactly the same time (to the second). Kirbycide, Ganoncide, Dededecide or Bowsercide can easily create this situation in two player matches, and having all characters on a horizontal platform in Icicle Mountain in Melee can also do such. If all characters die at the same time in Sudden Death, then the winner is determined by port priority in the first 2 games; in Super Smash Bros., the player with the highest player number will win (i.e. if Player 3 and Player 4 tie in Sudden Death, Player 4 will win) and in Melee, the player with the lowest player number will win (i.e. if Player 1 and Player 2 tie in Sudden Death, Player 1 will win). This gives a negligible, but technically true, advantage to players with lower or higher player numbers. Tests have shown that the winner is decided at random in Brawl. In Super Smash Bros. for Nintendo 3DS/Wii U, the winner is whoever dealt the most damage throughout the match.