Screen KO is a term regarding a special type of KO in the Super Smash Bros games. Instead of being Star KO'd off the top blast line and flying away from the stage, the character appears to fly at the screen blocking a part of the view and hit the screen before falling down and being KO'd, which may be how Screen KO's got their name.
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 can determine the match.
The Screen KO was in the series since the original, sometimes top-KO'd characters would fall down between the stage and the camera, instead of flying away. Depending on the camera angle, this may not be seen. The distance from the camera is chosen randomly - sometimes the doomed character appears to be falling normally, while at other times their body is just a quick flash of color down the screen. Screen KO's in this game share their duration with a Star KO (about 2 seconds). But in Melee and Brawl it got recognized more, as the character actually bounced off the camera with a grunt sound before being KO'd, which means Screen KO's have their duration reduced.
In Super Smash Bros. for Nintendo 3DS/Wii U, the screen KO makes a triumphant return, this time the character freezes on the screen for a second, and the time between the screen-freeze and the actual KO has been increased, most likely to make it as long as a Star KO. More than 1 character can be Screen KO'd at the same time. Interestingly, no one even makes a grunt when they hit the screen.
In Super Smash Bros. for Nintendo 3DS/Wii U, many things were done to the Screen KO to try to make them rarer. First, there seems to be a knockback cap on both Star & Screen KOs. For example, if Mario were to be launched upward by a POW Block at 100%, there's a good chance he will be Star or Screen KO'd. However, if he was instead at 300% on his damage metre, he will almost always be Blast KO'd instead. The limit itself is unknown, however. Second, Star & Screen KOs no longer happen normally if there are less than 5 seconds in a match. This, however, can be bypassed by using Olimar's Final Smash during the countdown as Star & Screen KOs will still happen. Lastly, Screen KOs are rarer where Star KOs are disabled such as Delfino Plaza.
In Super Smash Bros. Ultimate, Screen KOs return, working as they did in SSBWU/3DS although the entire process is now much faster and their animation finishes with a Blast KO off the bottom blast line after the target slides off the screen. An interesting note is Bowser's final smash, Giga Bowser causes an automatic screen KO to fighters who are caught in it, though the target comes from the gameplay plane itself, not from the upper blast line. Screen KO's can also occur if the target was abducted by a Beetle.
- In Mario & Luigi: Superstar Saga, a similar Screen KO took place; near the end of the game, Bowser flew out of his castle and hit the "screen", cracking it and sliding off the glass. This may be where Screen KO's trace their origin to.
- If a character is Screen KO'd on a large stage in Super Smash Bros. Brawl (for example, 75m or New Pork City), then a player can pause and zoom out the camera and see the character hitting the screen right before they are KO'd. This will not work on smaller stages, however.
- In Brawl, characters do not yell out as loud as they did in Melee when they hit the screen. A majority of the characters are barely heard when they hit the screen in Brawl.
- The Screen KO actually takes longer than a Star KO in Super Smash Bros. for Nintendo 3DS/Wii U, but only milliseconds longer.
- In all games, you will respawn faster than if you got KO'd another way.
- Kirby has the three different facial expressions with the Screen KO.
- Mario's facial expression, whenever he is Screen KO'd, is different between the 3DS/Wii U versions.
- In Super Smash Bros. for Nintendo 3DS/Wii U, Shulk is the only character who has his back to the screen when being Screen KO'd. This shows his current Monado Art.
- Bowser, Donkey Kong, and King K. Rool fall back when they suffer Screen KO's.