A sacrificial KO (also called a kamikaze or a suicide) is a technique that has appeared in all installments of the Super Smash Bros series, where one character KOs both him or herself and an opponent with a single move. In most cases, this involves grabbing the opponent and dragging him/her downwards to the bottom blast line, though self-damaging attacks can also prove effective. 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.
In Smash 4, most sacrificial KOs were nerfed so that an attempted sacrificial KO causes the attacker to be KO'd before the victim, potentially allowing the victim to return to the stage if their recovery is good enough and making sacrificial KOs much less useful. This discourages the abuse of special moves to perform a sacrificial KO to win a game. The only exception to this rule is Ganondorf's Flame Choke, as it is more commonly used as Ganondorf's only decent horizontal recovery option, and would see no use off-stage if it caused Ganondorf to be KO'd first.
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 t1mmy and his machinima entitled "1-800-KIRBYCIDE".
Grab-based sacrificial KOs
Other sacrificial KOs
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 a minority of 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.