KO

A KO, short for knock-out, is the term for when a character loses a stock or a point in the ' series and the ' series. A knock-out occurs when a character touches a stage's blast line, usually as a result of being attacked by another character or running off by themselves.

After a KO, the character is sent to their revival platform. In stock mode, if the character is KO'd after their last stock, they will no longer revive, and if there is only one other character left, the game ends.

There are three different types of KOs: the Blast KO, Star KO, and Screen KO. There is a fair bit of controversy surrounding the idea that, since the choice of Star KO and Screen KO is random, two players may end up being KO'd at different times, even though they hit the top blast line at the same time. If both players are on their last stock, this could determine the match.

Star KO
A Star KO is a type of KO in Super Smash Flash 2 in which opponents are knocked out by passing the ceiling, tumbling and falling in the background while screaming, emanating music notes, or yelling, eventually disappearing as a star. Characters who have above-average accelerated falling speed are less susceptible to this then characters with below-average falling speeds. This type of KO has been present in all of the Super Smash Bros. games.

Screen KO
A Screen KO is a type of KO in the Super Smash Bros. series and Super Smash Flash 2 where a character falls and crashes into the screen, while making a sound, when they are sent flying above the top blast line. Unlike in the main Super Smash Bros. games, up until, where characters normally hit the screen with their back, in Super Smash Flash 2, characters hit the screen with their front. The screen will also crack, adding to the effect that the character is breaking the camera. Additionally, only one character can be Screen KO'd at a time, as all other vertical KOs will be Star KOs until the Screen KO is finished.

Self-destruct
A self-destruct, often abbreviated SD or referred to as suicide, is the term for when a character gets KO'd without being hit by opponents. A self-destruct may occur to a player in Super Smash Flash if they touch the stage's blast line without being hit in the air or into the blast line, while in Super Smash Flash 2 it only occurs if the KO'd player was not hit by an opponent during the stock. It may also occur if the player gets KO'd by a stage hazard.

Each self-destruct subtracts one point from the player's score. While Super Smash Flash counts each self-destruct as a fall (only the falls are included in the score), Super Smash Flash 2 counts self-destructs and falls separately.

Super Smash Flash includes two bonuses related to self-destructs: "SDs", which penalizes 500 points for every self-destruct the player commits, and "Self-Destructor", which penalizes 2000 point when player repeatedly SDs in a match.

Sacrificial KO
Some characters have the ability to KO themselves and an opponent with a single move. This is called a Sacrificial KO. In most cases, this involves grabbing the opponent and dragging them downwards to the bottom blast line. Those are impossible to perform in Super Smash Flash, due to characters being unable to grab or throw.

One-hit KO
Some attacks, most notably a Home-Run Bat swing, can KO an opponent at 0% from center stage. Attacks of this strength are said to be able to one-hit KOing — OHKO for short — an opponent.

In Super Smash Flash, there are no OHKO attacks, as hitboxes have a constant, per-frame damage output rather than a single set value. However, instant-KO attacks are commonly erroneously referred to as OHKOs regardless.