Sacrificial KO

For Hero's suicide attack, see Kamikazee. A sacrificial KO (also called a kamikaze, a suicide or a trade-off) is a technique that has appeared in all installments of the  series, where one character KOs both themselves and an opponent with a single move. A majority of sacrificial KOs involves attacks that can grab opponents in midair, though a number of other attacks, such as stall-then-fall aerials and self-damaging attacks with self-knockback, can also be considered sacrificial KOs. Most sacrificial KOs result in the user self destructing, either by directly KOing them alongside the opponent or by preventing them from potentially returning to the stage.

Sacrificial KOs are useful if the user has a high percentage and the opponent has a low percentage; as the user is likely to be KOed soon, taking down a comparatively fresh opponent at the same time can even out the match. If the user has a lead in stocks, sacrificial KOs accelerate the match and can even score victories if the victim only has one stock remaining. In the same way, low-damage or trailing players should avoid using sacrificial KOs, as this simply brings them closer to losing. If both players have only one stock remaining, then the user can win, lose, or enter Sudden Death, depending on the exact characteristics of the individual technique.

While sacrificial KOs returned in Smash 4 with the same functionality as before, version 1.0.4 nerfed a majority of these KOs by causing the initiator to be KOed before their victim, potentially allowing the victim to return to the stage and making sacrificial KOs much less useful for winning matches. Before Ultimate, the only exception to this rule was Ganondorf's Flame Choke, as it is more commonly used as Ganondorf's only decent horizontal recovery option, and would see little to no use off-stage if it caused Ganondorf to be KOed first. In Ultimate, Flame Choke was nerfed to KO Ganondorf first; however, every sacrificial KO that used a meteor smash was made more reliable, often KOing the opponent before the initiator, due to meteor smashes KOing characters before they hit the bottom blast line if the knockback is strong enough.

Sacrificial KOs are typically named by combining the suffix "-cide" with the first part of the character's name; this convention was popularised by American smasher and his machinima entitled "1-800-KIRBYCIDE".

Other

 * Risky meteor smashes or off-stage aerials generally do not count as sacrificial KOs; the term implies that it is the move that KOs the user, not the fact that the user could not recover after using the move. It should be noted that with stall-then-fall attacks the user is nearly guaranteed to be KO'd unless they perform the aerial very high up.
 * Using a move that KOs an opponent in addition to one's teammate (or one's partner Ice Climber) can be considered a sacrificial KO in some ways, with the main difference being that it is not self-sacrificial.
 * Sometimes, Olimar's Pikmin-based attacks will require him to throw a Pikmin off the ledge in order to land a KO. In this case, the loss for Olimar is not equivalent to stock, and it is generally not considered a sacrificial KO, though it involves a level of "sacrifice".
 * Though very uncommon due to how it's set up, characters with throws that send them and their opponents briefly above the upper blast line (Charizard, Kirby, and Meta Knight) can be used to perform a Sacrificial KO if an item or projectile acts on the characters at the apex of the throw. An example is if Mega Man's Crash Bomber is attached to either character and explodes at the right time during the throw.

In tournament play
While rare due to a relatively limited character pool, sacrificial KOs have their own rules within tournaments: if both the victim and initiator are KOed on their last stock because of a sacrificial KO, the results screen is ignored and the initiator is deemed the winner. This rule, however, has been disputed, with some players claiming that the winner of the game should be determined by the game and not by observers.

Additionally, as mentioned earlier for Smash 4, every character except Ganondorf releases their opponent after they SD, allowing some characters to return to the stage, making this ruling even more questionable. One rule that is seen in some tournaments states that if both players die at the same time (whether a sacrificial KO or not), a tiebreaker match (usually 1 stock, 3 minutes) is to be played on the same stage played before to determine the official winner of the match, ignoring sudden death altogether. Another rule that forgoes tiebreaker matches favors the initiator if the KO results in Sudden Death, but the win is otherwise awarded to whoever is declared the winner on the results screen.

Trivia

 * If a Sacrificial KO is performed on a Subspacial clone in the Great Maze while the player is on their last stock and holding an item, the player will reappear in the area they were previously in, no music will be played, and after a few seconds, the screen fades into the Continue screen.