One-hit KO

A one-hit KO, commonly abbreviated as OHKO (also referred to as an Instant KO in Melee), is an attack in the Super Smash Bros. games with such high base knockback, that it KOs at 0%. However, moves that can OHKO are not necessarily guaranteed to do so, and may fail to OHKO under the following circumstances.

• The opponent techs, DIs, utilises momentum cancelling, and/or crouch cancels.
• The opponent hits into a wall, which absorbs enough knockback to prevent the OHKO.
• Knockback may be insufficient to KO at 0% on very large stages (e.g. Hyrule Temple, New Pork City, 75 m.).
• Knockback may be insufficient to KO at 0% if the attack had been landed previously (due to Stale-Move Negation).
• Knockback may be insufficient to KO heavy characters at 0%.
• Opponents are under an effect that makes them more resilient (such as being giant, metal, or in an event that reduces the knockback they sustain), or the player is weakened (such as being tiny or given a lower handicap).
• The damage ratio is lower than standard, reducing knockback.

The general rule for a move to be considered a one-hit KO is being able to KO the majority of characters from the center of Final Destination at 0% in its normal trajectory without any outside factors affecting the knockback. Another common standard is to compare the move to the smash attack of the Home-Run Bat, the move intended to be the quintessential OHKO by the programmers.

In Super Smash Bros. 64

Moves that KO'd at 0% were almost nonexistent in the original Smash. In fact, only two moves in the game can OHKO without the aid of any modifiers.

• A smash attack with the Home-Run Bat.
• Getting hit by a walking Bob-omb after being reflected by Fox's Reflector.

In Super Smash Bros. Melee

Unlike in Smash 64, there are multiple moves that can OHKO in Melee. They still remain rare however.

• Roy's fully charged Flare Blade.
• Mr. Game & Watch's fully loaded Oil Panic after absorbing three strong enough projectiles (Such as three PK Flashes).
• Roy's Counter upon countering an extremely powerful attack; a hitbox that deals around 35% damage will result in an OHKO if countered.
• A smash attack with the Home-Run Bat.
• Getting caught in Lugia's Aeroblast.
• Touching Moltres.
• Banzai Bill's explosion on Princess Peach's Castle (if all hits connect).
• A thrown Polar Bear.

In Super Smash Bros. Brawl

Brawl continued the trend of adding many OHKOs into the game. However, they almost all were Final Smashes, item related, stage hazards, or boss attacks.

• Mr. Game & Watch's fully loaded Oil Panic after absorbing three strong enough projectiles.
• Ike's stage 8 Eruption.
• Ike's Counter upon countering a ridiculously powerful attack; a hitbox that deals around 45% damage will result in an OHKO if countered. Marth's Counter can also potentially inflict an OHKO, though it must reflect an even more powerful move (a hitbox that deals around 50% damage).
• Marth's Critical Hit.
• Ganondorf's Beast Ganon (If all hitboxes land). If a character paralyzed by Beast Ganon is not hit by the charge afterward, they will be inflicted with a meteor smash of OHKO power.
• Wario-Man's fully charged Wario Waft.
• Lucario's Aura Storm at full power when all hits connect.
• Zelda's Light Arrow (barely in OHKO threshold, easily DIed).
• A smash attack with the Home-Run Bat.
• The Dragoon.
• If the Hothead is powered up significantly (e.g. through multiple reflections), it can deal well over 200% damage and OHKO.
• If a Soccer Ball is launched at enough speed (after either being hit by an extremely powerful attack such as a Home Run bat swing, or being launched after receiving enough damage), it will OHKO anyone it slams into.
• Touching Moltres.
• Suicune's Aurora Beam.
• Deoxys's Hyper Beam, both the single initial blast and the following multi-hitting blast.
• Electrode's explosion after being smash thrown.
• Knuckle Joe's Vulcan Jab to Rising Break attack.
• If Wario runs over a buried Pitfall while riding on his Wario Bike, he will be sent flying at OHKO power.
• Touching the hull of the Pirate Ship.
• The Ultimate Chimera's bite.
• The first spike on Rumble Falls (can easily be teched).
• Getting crushed in the Subspace Emissary.
• Tabuu's Off Waves (on Normal or higher difficulties in Subspace Emissary) (Very Hard and Intense in Boss Battle Mode).
• Tabuu's Golden Brackets attack on Intense difficulty in the SSE.
• Galleom's attack when he stiffens and falls on the player on Intense difficulty in the SSE.
• Galleom's tornado spin on Intense difficulty in the SSE (if most hits connect).
• Luigi's down taunt when it's a Meteor Smash.

Video

The following video demonstrates all the moves and hazards that KO at 0% in Brawl.

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In Super Smash Bros. 4

Like Brawl, SSB4 continues to add OHKOs to the game.

• A smash attack with the Home-Run Bat.
• The Daybreak's sweet spot.
• The Dragoon.
• Master Core's final attack if the player doesn't destroy it in time.
• Mr. Game & Watch's fully loaded Oil Panic after absorbing one strong enough projectile.
• Marth and Lucina's Critical Hit.
• Electrode's explosion after being smash thrown.
• Touching an Orne.
• Giga Mac's fully charged Straight Lunge sweetspot.

Trivia

• The smash attack with the Home-Run Bat is the only attack to be an OHKO in all four installments of the Super Smash Bros. series.