Instant KO

An instant KO is a type of KO which occurs instantaneously and in-place, without the fighter passing a blast line or being launched at all. A character suffering an instant KO will disappear into a colorful starburst explosion and then (if they have any stocks left) respawn as normal. Instant KOs were introduced as stage hazards in Super Smash Bros. Brawl, and a greater variety of attacks and conditions causing instant KOs were added in Super Smash Bros. 4 and Super Smash Bros. Ultimate, the latter game introducing instant variations of Screen KOs, Blast zone and Star KOs. Several instant KOs require the opponent to be at a certain damage threshold in order to be instantly KO'd; otherwise they will be launched as usual.

Stage hazards

 * Several levels in The Subspace Emissary feature moving walls, blocks, elevators, and similar solid platforms. If they are caught between two of these objects as they collide together, the player will be crushed and instantly KO'd.

Final Smashes

 * If 's Infernal Climax completes, any opponent caught by Gomorrah with 100% or more damage at the end of the attack will be instantly KO'd.

Enemies

 * Orne, an enemy found in Smash Run, instantly KOs fighters on contact with its Obliviate effect.

Stage hazards

 * Danger Zones in Smash Run instantly KO the player regardless of damage.
 * Danger Zones in The Great Cave Offensive damage and launch players similarly to lava; if they have 100% or more damage, however, the player will be instantly KO'd.
 * The interior of Master Fortress is lined with acid-like Danger Zones which cause an instant KO at or above 100% damage.
 * On Midgar, when the main platform is cleaved apart by Odin, the two halves of the stage will eventually reconnect. Any fighter caught in the middle when this happens will be crushed.
 * When Midgar is flooded by Leviathan, opponents with 100% or more damage will be instantly KO'd if the current sweeps them into the right side of the stage.

Playable characters' standard moves

 * 's Kamikazee uniquely instantly KO's himself, damaging foes caught in the blast.
 * Hero's Metal Slash will instantly KO metal opponents and an opposing Hero under the effect of Kaclang.
 * Hero's Whack and Thwack have a chance to instantly KO an opponent, with a higher probability the higher both the user and opponent's percentages are.

Final Smashes

 * 's Infernal Climax behaves as it did in Smash 4.
 * 's Giga Bowser Punch can instantly Screen KO, blast zone, or Star KO fighters with 60% or more after being punched (80% when using the weaker version via FS Meter).
 * 's Triforce of Wisdom can instantly KO fighters with 100% or more damage at the end of its animation.
 * 's Octopus instantly KOs fighters caught in its tentacles upon reaching the side blast zone, if the opponent has not died off the side already.
 * 's Plasma Scream can instantly KO fighters with 100% or more damage at the end of its animation.
 * 's All-Out Attack can instantly KO fighters with 100% or more damage at the end of its animation. If the last stock is taken with this attack, the game instantly ends and a unique victory screen is played.
 * 's Sealing the Keyhole can instantly KO fighters with 100% or more damage at the end of its animation.

Items

 * Poké Ball summon Mimikyu will instantly KO the fighter it grabs hold of if they reach 90% damage after its attack.
 * Death's Scythe will instantly KO when striking a fighter at or above 70% damage with the tip of the scythe using a fully charged smash attack, 80% damage using an uncharged smash attack, and 120% using a tilt attack.

Stage hazards

 * Returning stage Midgar features the same crushing and flood hazards it had in Smash 4.
 * Returning stage The Great Cave Offensive features the same Danger Zones it had in for Wii U.
 * New Pork City is a returning stage with a new hazard: the bite of the Ultimate Chimera now instantly KOs fighters, instead of imparting extreme knockback as it did in Brawl.
 * The Red Bulborb on returning stage Distant Planet instantly KOs fighters with its bite, instead of carrying them off screen as in previous games.

Other

 * Ultimate is the first game in the series where Stamina Mode can be played with multiple stocks. Under these conditions, fighters who lose all HP with more than one stock left suffer an instant KO and respawn, taking away one stock. When the last stock is lost, the standard Stamina Mode KO occurs with the fighter falling to the ground and lying there motionless, then exploding and disappearing for good (unless they can use Share stock in a team battle) after a short pause.

Trivia

 * In SSB4 and Ultimate, when he is instant KO'd, Mega Man has a unique animation where he explodes into orbs and makes the same sound as when he dies in his home series (this also occurs when he is blast KO'd). In Ultimate, also has a unique instant KO animation; they burst into a puddle of ink and their squid-shaped spirit flies upward briefly before disappearing, as in the  games.