One hit knockout

A One hit knockout (OHKO) is a term used for character attack's that, if successful, knocks the other player out instantly.

These are usually achieved by setting the opponent's health to zero if the attack connects, resulting in an instant kill that cannot be survived regardless of health or defense level.

This is widely discouraged throughout the M.U.G.E.N community, unless the attack is originally part of the movelist of a character which is being ported to M.U.G.E.N, such as those in Fist of the North Star or Guilty Gear.

Examples

 * Doraemon Second and Third Dorayaki attack
 * Every Guilty Gear and Fist of the North Star character's Instant Kill
 * Crazy Catastrophe's Cremination Blast
 * Almost all of Ironcommando's characters have at least one, and it is usually unblockable, hard to avoid, or both.
 * Dancing Banana's Shun "Banana" Satsu.
 * Mosquitoes' Blood Slaughter.
 * Hell House's Hell Press.
 * 20000's X-Termination, Pulver Bomb, Nucleon Cannon EX and Cyber Crash.
 * Mecha Scorpio's Scorpion Goku Satsu and Scorpion King.
 * Christmas Tree's TIMBERRRRRR and "Merry  Christmas".
 * A-Bomb's basic attack.
 * Mecharoid Soldier's Suicide Truck.
 * Space Invader's basic attack.
 * Hatsune Miku's Miku Miku Ni Shite Ageru
 * All BazBlue's characters
 * All Guilty Gear's characters.
 * The Dopefish's "Eat" move.
 * Broccalon´s "Green Eggs and Ham" Attack
 * Mortal Kombat characters fatalities.
 * Jolteon's Thunder.
 * Flareon's Overheat.
 * Glaceon's Sheer Cold.
 * God Orochi's Celestial Star.
 * Most of Hastur's Supers.
 * Apollo Mizuchi's Shattering Glass move.
 * Pingu's Super Scary Attack & Pin-Goku-Satsu.
 * Rare Akuma's Raging Demon
 * Jellypus's Tentacle Super
 * Master Mecha Sonic's Hyper Kame Wave
 * The F1 key (character)
 * ONI-MIKO-ZERO (character)
 * ONI-MIKO-R Moves. Including her 12p mode.
 * Guanyin & similar characters
 * Seigyoku Raptor's EX Energy Wave
 * Neo Meep140's Doomsday Beam
 * Chuck Norris's specials moves
 * Most of ALSIEL's super moves
 * Yogurty14's Nyan Cat
 * Mr. Game and Watch's Judge (providing it displays a "9")
 * Sman's 100 Crack Fist.
 * Giygas's Death Traps if you do not escape
 * All of Sonic.exe's moves.
 * G-Mizuchi's Darkja (Black Hole)
 * G-Orochi's Holyja
 * Most of supers of Alosson's edit of Omega Tom Hanks
 * Omega Tiger Woods's Universal Distortion
 * Dark Donald's Darkja
 * Most of R-Masamune's supers
 * Shotofusion's infamous unknown move
 * Annoying Orange's wazzup
 * Some of the Ronald McDonald cheap edits
 * Heart Aino, Saki Tsuzura and Weiss by Flowrallia
 * Reimu Hakurei's "Fantasy Heaven"
 * Flandre Scarlet's "And Then There Will Be None"
 * Yuyuko Saigyouji's "Invocation of Death" (RicePigeon's version only)
 * SNS and Pingurules Luigi's taunt
 * Ronald-dool's strong-down-kick
 * NeinCatAGK Giant Angry German Kid And EX Nikki McDonald (11TH Pallete)
 * Anyone with the name %v%v on it will OHKO other cheapies in winmugen if debug mode is active.
 * Pac-Man Delta's Level 2 Rush Attack Hyper, Shun Goku Satsu, and Super Pac Beam
 * Norman's H-Bomb attack
 * 1 Up Mushroom by bumping into people
 * High Speed Mario's Buddha attack
 * Old Bloo's Shun Goku Satsu
 * Y Kun's Pistol attack
 * New Spelunker's Shun Goku Satsu
 * Funny Echizen's door attack
 * LS's Doomsday's Level 3
 * Stickman14's Luigi's Shun Goku Satsu(And BIS Mario and Luigi, since they are spriteswaps of him.)
 * Every attack of Shin Original The Character.
 * D4 Kirby's Mega Sword attack.
 * Fosh Beary's "Fuck this Planet" hyper.

"Untrue" one hit knockouts
Certain attacks aren't true one hit knockouts, but cannot be survived by normal characters.

These attacks usually deal a fixed amount of damage, usually a very high amount, that will easily deplete 1000 to 2000 life on most characters, even with significant defense multipliers. However, by artificially setting the character's defense or health to a very high level, it would be possible for the character to survive the attack.

An example is Metool's Giant Metool drop, AKA, and 0WN3D, which does 9000 damage, a possible reference to the "Over 9000" fad. Most overpowered Dragon Ball Z characters who have energy waves that deal damage at a constant rate instead of one extremely strong blow.

Infinite attacks that, unless halted, put the opponent into a constant hit state loop can also be classified as untrue one hit knockouts. An example would include Psyqhical's Energy Pillar in the corner.