KO

A KO, short for knock-out or knock-off, commonly known as a death or a kill or even a finishing blow by Stamina Mode, occurs when a player is launched beyond the stage's blast lines by the opponent's actions used in the Super Smash Bros. series. The KO'd player is sent to a revival platform to re-enter the match. Losing all HP in Stamina Mode results in a KO without crossing a blast line, and some attacks and hazards can cause instant KOs without the target crossing the blast line or being launched at all.

All characters have the same KO explosion, namely, a gigantic colorful blast that extends in the direction the victim was KO'd, in the color of the player's port: Player One's explosion is red, Player Two's is blue, CPUs are grey, and so on. Only two characters have slightly different KO explosions, Mega Man and Luma: Mega Man will split up into orbs the color of his costume (alongside the normal explosion), like he does when he dies in the Mega Man series (they will sometimes not appear if many Mega Mans are KO'd at the same time), while Luma's explosion is smaller and creates colorful stars. A one-hit KO occurs when the target suffers a KO even when their damage is at 0%, while an instant KO completely bypasses knockback and damage.

Once KO'd, the following may then happen depending on the type of match:
 * In a Time match, the KO'd player loses a point, while the player who made the KO gains a point.
 * In Super Smash Bros. and Super Smash Bros. Ultimate, the score indicators are present in both Time and Stock matches but are meaningless in the latter. In other games, the indicators are absent for Stock matches.
 * In a Stock match, the KO'd player loses a stock. If players lose all their stocks, they will receive the following:
 * Single-player: A Continue or a Game Over (the latter if the player doesn't have enough s in Super Smash Bros. Melee and Super Smash Bros. Brawl or chooses not to continue).
 * Multiplayer: Removal from the rest of the match. In a team match, the player can "borrow" a stock from an ally.
 * In a Coin Battle, KO'd players lose half their smash coins, rounded down. Brawl prevents a player from losing more than 100 smash coins at once. The lost coinage flies into play if the KO was made off the side.
 * In a match (Melee only), a KO will earn the player 500 points, while a fall will subtract 500 points.
 * In the Subspace Emissary, the next character in the lineup is loaded and teleported into play without a revival platform. One stock is also lost.
 * Characters can also be KO'd in the Subspace Emissary if they are crushed by moving walls, ceilings, or floors.

KO property
In Super Smash Bros. and Melee, each character has a "KO property" which starts out empty. When characters are hit by any attack (be it a physical attack, a projectile, an item, etc.), their KO property is set to match whoever made the hit. Stage elements do not change the KO property. The KO property is reset once a character lands on the ground and is no longer moving as a result of the attack's knockback. When the character is KO'd, the KO goes to whoever matches the KO property. If the property is empty, the KO counts as a self-destruct. In simple terms, it goes to whoever made the last hit.

However, this format was altered for Super Smash Bros. Brawl. In Brawl, a character's KO property is only reset 3 minutes after landing on the ground. This essentially means that a character must refrain from being hit for 3 minutes for a self-destruct to actually count as such; otherwise, a self-destruct will be credited as another player's KO. While this was possibly implemented to avoid griefing in online matches (by self-destructing simply to deprive other players of points), in reality, its main effect is giving other players illegitimate points, as it's clear that jumping off the edge a few seconds after successfully recovering is not a KO.

There are exceptions, however, particularly during most Final Smashes. If players jump off the stage during a Final Smash such as, then, unless someone else hit them before landing, it will count towards the user of the Final Smash, instead of the last one to hit them (Samus in this case). Moreover, getting KO'd during the usage of certain Final Smashes such as will result in a self-destruct instead of a KO, even if players have been damaged by opponents previously. Characters with invincibility from a will also self-destruct instead of being KO'd.

Super Smash Bros. 4 appears to retain the Brawl system, but with one notable change: in matches of two players, any self-destructs are also credited as KOs for the opponent. For example, if a player has been KO'd once and has one self-destruct, the opponent will be credited with two KOs. This change only affects KO-based statistics; it has no real effect on who wins the match. A cannon resets the KO property as well. For example, if a player got knocked into a cannon on a custom stage and dies because the cannon shoots them past the blast line, it will count as an SD.

KO sounds
In addition to the colorful KO blast, every fighter makes a loud, distinct vocal sound upon being KO'd, though there are some exceptions who are silent due to lacking voice lines. Throughout the series, these exceptions are:
 * Piranha Plant
 * Steve
 * Samus (Brawl onwards; has a Star KO sound effect)
 * Dark Samus (has a Star KO sound effect)
 * Mr. Game & Watch (not in Melee or Ultimate; Star KO sound effect is still present in Brawl and SSB4)
 * Olimar
 * Villager
 * Isabelle
 * Little Mac (when using Wire-Frame Mac costumes)
 * Duck Hunt (has a Star KO sound effect)
 * Mega Man (excluding "8-bit explosion" sound effects)
 * Pac-Man (with the exception of Smash 4's StreetSmash, where he uses his original death sound from Pac-Man)
 * Mii Fighters (not in Ultimate if voice clips are set).

Every fighter in Brawl, Smash 4 and Ultimate possesses two KO sounds, with the second being rarer and often a short phrase or line (the second KO voice clip has a 1 in 6 chance of playing). However, there are a handful of characters with only one KO scream, which are:
 * Jigglypuff (due to the English voice being recycled from Smash 64 and Melee in all games; the German and French voice clips also follow this trait, but has two in Japanese)
 * Mewtwo (as a possible callback to Melee)
 * Roy (as a possible callback to Melee)
 * in Ultimate
 * The s with voice clips set in Ultimate
 * Bayonetta
 * Ridley
 * Sephiroth

StreetSmash gives Pac-Man a KO sound not heard normally. Notably, both of Ganondorf's KO voice line in Brawl and SSB4, female Corrin's and female Inkling's secondary KO voice lines are much longer than most other characters. Ultimate's Stamina Mode also uses one of these sounds for almost all characters except for, , , , , , , , , , and who instead use their heavy knockback cries, and  and , who use a unique voice clip. An instant KO from Hero's Kamikazee also always uses the primary KO voice clip. Another peculiarity specific to Ultimate is that, should a fighter be sent flying during their last stock and the current match end, their KO scream usually not play or play only very briefly.

List of unique KO lines
While most characters simply emit pain sounds of various kinds when KO'd, from Brawl onward, a few such as Pit and Robin can speak phrases. All of these are used as secondary KO clips. However, Zelda uses her main KO line, which is spoken in Japanese.

Byleth (Male): "Not my best!" ("", I was careless...!)

Byleth (Female): "Forgive me!" ("", I've got hurt...!)

Chrom: "Sorry!" ("", Darn...!)

Cloud: "" (Missed it...)

Corrin: "How... can this...?" ("", How can this...) (Female Corrin drags the line for much longer compared to Male Corrin.)

Dark Pit: "It's not over...!" ("", It's not over yet....!)

Joker: "What?!" ("", Sorry...!)

Lucina: "" (Must I fall here...?!) (only in Japanese version)

Mythra: "Seriously?" ("", I've been finished...)

Ness: "Ouch!"

Palutena: "Oh no!" ("", Oh dear...)

Pit: "I'm done for..." / "I'm finished..."  ("", I got hurt...)

Pokémon Trainer: "Dang it!" (♂: "", Dang it...!; ♀: "", No...!)

Pyra: "I'm sorry...!" (, I've been finished...)

Richter: "Why?!" ("", Dang it!)

Robin (Male): "Reckless fool...!" ("", I was careless...!)

Robin (Female): "I was careless...!" ("", I was careless...!)

Ryu: "What?" (, What?)

Shulk: "Not good!" ("", Not good!)

Simon: "Curses!" ("", Dang it...!)

Sonic: "Ouch...!" (only in Japanese version)

Sora: "Noooo!" ("", Oh no...!)

Terry: "Ouch!"

Wii Fit Trainer (Female): "Oops!" ("", What?) / "Wha-!?"

Zelda:  "" (Nooo!) (despite being the main KO line.)

Trivia

 * In Super Smash Bros., the sound effect that plays for the blast KO uses the same "ping!" sound effect from certain moves or items, albeit slowed down significantly.
 * In SSB4 and Ultimate, should a fighter be sent flying when extremely damaged (such as at 999%), their KO scream may not play and will be replaced by one of the fighter's "hurt" voice lines or nothing at all. This happens more frequently if the fighter is frozen, or if a character is hit right by a blast line.
 * In Ultimate, while the Screen KO uses the Blast KO effect at the end of the animation, Mega Man will not split up into orbs.