The boomerang from Link's Awakening, which you have to trade in your shovel for, can kill the final boss in a single hit if you aim for the eye. In the same game, stealing a product on a shop and coming back will show the owner zapping Link to death due to the theft.
In The Wind Waker, you will eventually get the Light Arrows, which are so powerful they obliterate ANY normal enemy in an explosion of light. For that matter, almost any time the Light Arrows are featured (Ocarina of Time is an exception because they only stun enemies). They OHK all normal enemies and are powerful enough to stun Ganondorf, The King of Evil.
Link can learn two sword techniques that do this. The Mortal Draw is tricky to use, and doesn't work on certain enemies that are defended in the front (you need another sword technique entirely for them), but it can still be effective in certain situations. Against bosses, it won't be an instant-kill, but it will hurt like hell!. The other technique is the Ending Blow, which delivers a deadly stab at enemies when they're knocked down in the floor after being attacked; it can be used against bosses and it does kill them instantly (in fact, the Final Bosshas to be killed with this technique, he won't die otherwise).
Twilight Princess also has a one-hit kill against Link regarding the Zora Armor. The armor is weak to fire and ice attacks, which makes Link take double damage, but if he falls into lava or a near-frozen lake with the armor on, it's instant death — regardless of how many hearts you have. Notably, Argorok's fire breath is powerful enough to become an instant-kill attack while the Zora Armor is in use.
In Spirit Tracks, the Dark and Armored Trains can kill Link instantly if he fails to dodge them while travelling with the Spirit Train.
The Guardians patrolling the Silent Realm can kill Link instantly. The fact that they are only found in the Silent Realm, where Link loses access to his sword, can make encounters with them rather tense.
There are three examples of obstacles that, instead of simply making Link reappear at the start of the room where they hit him (a tradition for the series), they actually kill him: The giant rolling boulder in the Earth Temple, the statue of Buddha in Ancient Cistern that descends when Link gets the Boss Key, and the lava overflowing a certain underground passage in Fire Sanctuary.
As in Twilight Princess, the Ending Blow allows instant kill to enemies when it's executed well.
Count Vladmu a.k.a. Flash has his namesake ability, signaled with flames at his feet before he parts his robe and glows brightly. If you so much as look his way during this, you either forfeit a doll (Chelsea automatically, Bunny on Recall) or head back to your last save point. Direct contact with his head by anything other than the girls' feet is also instant death.
Chelsea, as a boss, has a mode where crosshairs lock onto you. If you stay in one spot too long, you get a headshot, which kills you no matter how much health you have.
Dechronos!Bunny throws BFSes on the last ten to fifteen percent of her health. Touching one effectively paralyzes Chelsea while Bunny beats a doll out of her. What, don't have a doll? Say hello to the last save point, sucker! Oh, and don't touch her at this time, either.
In most 2D games, the Screw Attack is lethal for non-boss creatures. It's a reason why it's often obtained late.
Metroid Prime Hunters in multiplayer mode has the Omega Cannon, a weapon so powerful that it will kill anyone, including the shooter, in a single hit because the blast radius is so damn large. The weapon can only be used once and you have to pick up another if you want it again. It only appears in one level and people generally avoid picking the level it appears in since it becomes a race to the top to see who can get the weapon first. Naturally, people who cheat will love to use this weapon.
Metroid Prime 3: Corruption also has an example in the Nova Beam. By itself, the Nova Beam is just a high-frequency weapon that can damage enemies regardless of special Phazite armor they may be wearing. Use it in conjunction with the previously gained X-Ray Visor though, and you can start targeting some enemies' internal organs for instant kills.
Certain bosses in the Tomb Raider franchise can do this: Puna in III attacks with instant-death lightning, although it can easily be dodged, and the Final Boss of the same game will shoot an undodgeable instant-kill fireball if it gets in range. In the games where it appears, the T-Rex can swallow Lara whole.
In Contra'sSpiritual SuccessorHard Corps: Uprising, enemy snipers will attempt to lock onto you, and if you get caught in the crosshairs, they'll fire a bullet that does 4 points of damage if it connects, enough to kill any character in Arcade mode but it can be survived in Rising mode thanks to life upgrades (most other attacks only deal one point of damage to your Life Meter).
Several enemies in Zombies Ate My Neighbors could be taken out with one shot of the right weapon. Some were damned obvious (use silverware on the werewolves or the footballs on football players), some were pure Guide Dang It (using the Martian Bubble Gun on the giant ants or the tomatoes on the Martians).
In the online game Bearbarians, abusing the combo rules and an A.I. Breaker (or just being really good at hitting and running) can lead to your previously low to moderate damage getting stacked up high enough to insta-murder your opponents in a single blow. Combos increase your damage by 1 per consecutive unblocked hit, so a 50-damage attack becomes 51, 52 and so on, but are broken when an opponent successfully blocks. If you can find a location where the AI has to jump up, which renders it unable to block, carefully timed mashing of the attack button will allow you to stack up ridiculously long combos, leading to completely insane raw damage. 1000+ damage per hit will instantly massacre even the most durable opponent. Doing so while holding the enemy flag in a Capture the Flag match will ensure that the battle doesn't necessarily have to end until you develop carpal tunnel syndrome, fall asleep on the keys, or level up while standing atop a gore-soaked platform with more than 600 kills in just that level.
In the fourth level of Renegade, you have to beat up four mooks armed with knives. And then three more of them, accompanied by a mob boss. Who has a gun. No, you can't pick up weapons. Have fun.
The Killer Rabbit boss in Dragon's Crown once it Turns Red. It gains a move where it charges up a red aura, then leaps at a character. If this connects, it deals damage equal to the character's max health, and an x-ray of the character's skull breaking appears. Ouch. It can be survivable if your character gets their health above the maximum amount, though.
One Finger Death Punch plays this trope in the most essential manner, every normal Mook dies in one hit. The higher level enemies die in a couple of hits aswell (or dodge out of the way...or start a fighting sequence) but the average goon will just fall in one hit.
The infamous "Slots" spell almost always has an instant victory result, if you can time your button presses correctly (Though in the case of Selphie's "The End" and "Rapture", and Lady Luck's CONGRATS!, you don't actually kill the opponent. They just sort of go away). All Slots techniques bar Selphie's also have the chance to cast the same instant death spell on your own party, often with the result being just one reel off.
Final Fantasy I probably featured the largest variety of one-hit kill spells as standard black magic, several of which actually were very effective against specific monster types (even more as the party leveled up). There was also one enemy called 'Sorcerer' (named 'Mind Flayer' in the remakes) whose physical attacks inflicted only Scratch Damage but with a side effect of instant KO — pray they don't get to strike first when you encounter a group of 5. The ProRing, despite being obscenely expensive, protects against instant death, and renders Sorcerers completely impotent, but the game doesn't tell you that, ever.
The game has a trick that can make the Doom spell 100% effective on most enemies. This includes most bosses. However, it was corrected for the GBA version. There are also some weapons (the Assassin's Dagger and the Ichigeki are two of them) that will randomly use a highly-accurate Death spell for free (along with a unique animation) when you attack with them.
The enemy ability "Repose" (previously known as "Calmness") used by the top-tier foe Rest in Kefka's One-Winged Angel transformation, as a final attack. The character must block it or suffer an instant kill.
Edgar's Air Anchor. It always hits enemies that aren't immune, and when it does, the enemy gets one more turn before instantly dying.
Most instant death attacks do not work on The Undead, which regenerate to full health when struck by one. However, in Final Fantasy VI there are a few abilities that kill an enemy Deader than Dead, shown by an animation of the enemy disintegrating to tiny bits. The Odin and Raiden summons, Cyan's ultimate sword technique and the Scimitar/Zantetsuken weapon are the only four that can one-hit kill even undead foes.
The Tonberries creep slowly towards you then stab you to death. In some cases, it's not an instant death attack, but just does obscene amounts of damage. Later versions added the "Karma" ability, which deals damage equal to the amount of enemies a character has landed the killing blow on, sometimes with a positive modifier (i.e. number of killing blows x10, x20 etc). This can lead to odd circumstances where your main character is OHK Oed, but your White Mage or a party member you haven't been using much takes very little damage if any at all.
From Final Fantasy IX, Zidane's Soul Blade move, which gives the target the status effect of the weapon equipped with 100% success rate (barring immunities). With the Masamune equipped, which has the Doom status effect, all you have to do is survive until the countdown runs out.
Kimahri's Doom Overdrive has a 100% success rate (again, barring immunities). Kimahri's Thrust Kick and Auron's Shooting Star Overdrives knock enemies right out of the battle. There's also Anima's Pain ability, which causes Death, and Yojimbo's Zanmato (NOT an Overdrive, despite what many people think) which instantly wins the battle for you and works on ANYTHING, even bosses. You have to pay a redonculous amount of Gil to make him use it in some cases, though. Lastly, many abilities can be customised with Deathstrike or Stonestrike, whichkills any enemy that doesn't have immunity to Death or Petrification with one hit. It also make catching many monsters much easier.
The "Roulette" Blue Magic, which chooses one victim among all the current combatants. Unblockable, but doesn't kill the undead (they regenerate, as it's an "instant death" effect).
Aside from Death spells and Zantetsuken, Final Fantasy IV has Globe/Object 199, which usually does profane amounts of damage instead of inflicting instant death. It's just the damage tends to be in excess of however much HP the target is expected to have, so it achieves the same effect. This is the reason you keep the Attack Node (Defense Node in the DS version instead) alive and blast away at the CPU once its counterpart is slagged.
There's also the Jumbo Cactuar's "10,000 Needles, which hits for 1 damage 10,000 times in a series where the HP Cap is 9,999. One game has an ability that allows you to exceed this cap, but the same game has a bonus boss called the Cactuar King with a 99,999 Needles attack. Guess what the boosted HP cap is.
Wild ARMS 2 played with this a little. There was an optional boss that would completely regenerate its health every three turns, and 75,000 HP is no number to scoff at in this game (The Superbosses have 100,000). While using an Instant Death ability seems counter-intuitive in a boss fight, it's actually the way he is supposed to be defeated.
The two magic users, Xhela and Mizuti, both had One Hit KO special moves. Xhela's was her level XIII special "Seal of Water" and Mizuti's was her level IX special "Planet Soul". There are also a few magnus that have death chance, and a few with 100% chance (such as the "Death" tarot card).
A few select enemies and bosses have this. For example, during the boss fight against Geldoblame after he touched the End Magnus, he has the ability Forfiet Your Life, which causes 100% chance of death unless you have some kind of resistance, which is hard to get by that point in the game.
The final boss in the PlayStation remake of Lunar: Eternal Blue has an attack that deals about 2,000 damage. Just for reference: if you're dedicated, you might have a single character who has more than 500 hit points.
The final boss of Lunar: The Silver Star also used that spell (Fate Storm), but unlike in the sequel, it just killed the target outright. Particularly bad because the boss in question could doublecast, and would always cast Fate Storm along with Hell Wave, a powerful attack-all spell that could easily leave you in critical condition. So you had to revive the dead person AND restore your entire party, unless you learned the pattern and prepared for it beforehand.
The final boss of the PSP remake of Lunar: The Silver Star punishes the player for abusing Mist Barrier by casting a spell that makes his next spell deal 2,000 HP to the entire party on the last turn it's active.
The final boss Xemnas can attempt to grab Sora, which can only be avoided with invulnerability from something like Reflect or a limit attack. Should he succeed, he'll attempt to rip out his heart. Riku can save Sora from this, but if his HP is too low when he gets caught, you're out of luck, as it'll be completely impossible to stop it in time.
In the Final Mix version of the same game, Terra has an attack that is a bit like Heartless Angel; it rapidly drains your HP, and you have to push a button at the right time to stop it. Should you fail to do so, or push the wrong button? Instant death.
The final boss of Sora's story in Kingdom Hearts: Chain of Memories has Doom, in which you have six seconds to break six of his cards, or you die instantly. Combine that with the sleight that scatters your entire deck including your reload card, forcing you to pick them up again, and...
The Zantetsuken attack introduced in the final mix version of Kingdom Hearts I has a fairly high chance of OHKOing normal enemies. It becomes much more effective in later games with the addition of commands like Magnet and Zero Graviza that gather your enemies together.
PK Beam Gamma and PK Fire Omega from EarthBound Zero do this to one target or the whole party respectively.
PSI/PK Flash in EarthBound can do this. It's in the main character’s powerset and actually works on bosses. Should it fail, it typically leaves a status condition.
The "emit a glorious light" attack numerous enemies possess (Along with one of Giygas' "unknown" attacks) is actually a renamed PK Flash Gamma, and thus has a high chance of causing instant death to multiple party members, though thankfully, accessories that completely null the effects of PK Flash are rather readily available.
In MOTHER 3, the Upgraded Robots use the aforementioned glorious light, though there isn't any way to protect yourself from it this time.
The Ultimate Chimera instantly causes a game over when it reaches the party. They don't even get a chance to fight it.
Notably, PK Flash's instant death effect is one of only two ways you can beat the King Statue, which has a HP count of 100 million, versus the usual four digit HP count other bosses possess.
Geno from Super Mario RPG has an attack (the Geno Whirl) that deals 9999 HP of damage when timed just right. Since no enemy in the game, including bosses, has that much HP, that makes it a One Hit Kill attack. However, it does only minor damage to said bosses (except one: Exor, after losing his protection, so it comes in handy for players who consider him to be That One Boss), along with certain other enemies, namely the chest-based ones such as Box Boy.
Some enemies also have attacks that instantly kill the character hit by them unless said character is wearing an accessory that blocks them. Out of these attacks, some can be either fully or partially blocked if the player has good timing. One of the forms of the final boss has an instant kill which cannot be blocked be a Timed Hit. Of those that can be blocked, depending on your timing, you may either emerge unscathed, suffer an HP to One effect, or die.
In a partial aversion of the trope, numbered Phantasy Star games tend to feature a variety of these, often cheap to cast and geared to work on certain types of targets (inorganic or living). Even better, some of them are almost reliable! PSIV has a particularly large number of them; between techniques, skills, and combination attacks, nearly every character can kill some kind of enemy instantly. Played straight in that they don't work on bosses.
The games have the Mudo and Hama spells, both being single-target spells with 40% chance of inflicting instant death. Those are the weakest variants of the instant death spells in that particular franchise. Their most powerful forms, Mamudoon and Mahamaon, have a 60% chance of inflicting instant death on everyone in the party, yours or the enemies'. Of course, elemental affinities can mess with this. Both spells, however, also come in damage flavor. In the Digital Devil Saga series, Hama instead dealt a percentage of damage based on your current Health.
In most games, the most HP a single member of your party can have is 999; therefore any attack that hits for more than 999 HP is an instant kill. Shin Megami Tensei IV allows your party members to exceed 999 HP, but it's quite difficult to achieve, as only you, physical-based demons, and demons buffed with the Doping skill will be able to reach 1,000 HP.
Satan in Shin Megami Tensei II could just point his finger at someone, and the character would die. No chance of failure. The final boss only had to use his voice to do the same.
Demi-Fiend, from Digital Devil Saga, has Gaea Rage (also known as Game Over), that deals anywhere between 7,000 - 12,000 Almighty-elemental damage to your entire party. Again, HP cap is at 999.
Satan, again, in Digital Devil Saga 2, along with spamming Mamudoon on your party, has Retribution and God's Breath. God's Breath deals 9999 Almighty-elemental damage to everyone in your party. HP cap is at 999. You do the math. Retribution just plain instant kills a character, and is also Almighty-elemental, so no way of guarding from it.
Mitra, the second sector's boss, has Light of Order, which is a guaranteed instant kill towards a random demon. Thankfully it never targets you, but you'll still find yourself spending turns reviving demons (you need one turn to revive, then the next turn to bring them out to battle).
Attacks that cause Stone are effectively one-hit kill attacks. In the case of demons, the effect can be removed, but if you get hit with Stone, game over.
Beelzebub has Death Flies from this game onwards, an Almighty-elemental spell that deals plenty of damage and has 100% chance of instantly killing anything that doesn't nullify or repel Curse-elemental spells. The good news is that you may acquire said skill later in the game once you've leveled your Beelzebub adequately and in the Digital Devil Saga series.
Metatron, conversely, has the opposing move, Fire of Sinai. Massive Almighty-type damage, random chance of killing everything and anything not immune to Light spells, and it can hit twice due to the attack hitting random enemies.
Trumpeter has an Almighty-elemental skill called Evil Melody that deals instant death to the character with the lowest % of HP left.
Ahriman has a skill that will kill you if you don't play his game.
Eternal Rest instantly kills any character currently asleep in both parties.
God's Bow, a skill only White Rider has in Nocturne, kills anything not immune to Hama.
Another Rider, the Pale Rider, has Pestilence, a skill that inflicts Almighty damage and a chance of poison. Casting it with poisoned enemies will instantly kill them.
Stinger, one of Dante's moves in Nocturne, also has an instant kill factor.
Hell Gaze, another Death-elemental instant kill move.
In Persona 2: Eternal Punishment, there are lots and lots of instant death moves. Of course Hama and Death (called Light and Dark) but also many physical attacks, whether it's a main or added effect, various elemental combos that shouldn't be used on demons that can repel them and a few non elemental attacks that can be used by both your party and opponents. Some demons will use kamikaze instant death attacks. Phoenixes deserve a special mention as they will afterward revive their kamikaze fellows. Non elemental attacks like Multi Dimension will work on anything that isn't immune to instant death. Many are surprisingly effective. Death Roulette will do wonders on a single non boss opponent and will take care of those Boss in Mook Clothing. Some of them don't work that often but can't be blocked either and will help against those magic reflecting demons. Others will always kill anything... but at a price. Armageddon will do it for free but you can only use it in a New Game+ and you'll need loads and loads of money to obtain it. A few personas have the special ability to (sometimes) deal instant death to your opponent if the equipped character dies.
Two Persona have "Die for Me" and Samsara. They both act like Mudoon and Hamaon, respectively, except that the chance of success is more likely around 80% as opposed to 60%. And that's just against enemies with no weakness to it. "Die for Me!" and Samsara become Game Breakers in Persona 4. They have a 100% success rate to ANY enemy that doesn't resist/block/repel Dark or Light, respectively. Other that bosses, it's actually extremely rare to find normal shadows that block both light and dark.
Also in both games, the ability "Ghastly Wail" is instant, unavoidable death for any character afflicted with Fear. This also works on some bosses, such as P3's Strength and Fortune.
Another attack in Persona 4, "Summons to Yomi", is instant death to any character with any status ailment whatsoever. The enemy that uses that attack knows this, and likes to prefix it with one that afflicts party members with random status ailments.
Several Bonus Bosses also have an unofficial one-shot move, in the form of a modified Megidolaon that always deals 9999 damage in a game where the HP Cap is 999. Though they're programmed to only use it if you break the unwritten rules of the fight.
The Instant Kill attacks in BlazBlue have been un-nerfed even further, as all it takes is for your character to have a full SP meter in a deciding round, and it will take out any opponent, regardless of how much life they have left.
Naoto's Hamaon and Mudoon supers will instantly KO a foe if their "Fate" meter (which counts down from 13 when the opponent is hit by Naoto's gun or Persona attacks) is reduced to Zero.
Elizabeth has enhanced versions of these moves (Mahamaon and Mamudoon) which can be used at any time once she has enough SP, but they turn out to be Awesome, but Impractical because:
They have an absurdly long charge-up time and the opponent may not be in position once the spells activate, and
The spells disappear immediately if Elizabeth is hit (even while blocking).
The series has several moves that will knock the target out with a single hit: Guillotine, Horn Drill, Fissure, and Sheer Cold. They are balanced out by a very low accuracy, but they're still banned in Wi-Fi and online tournament matches. Also, Articuno learns both Mind Reader (makes the next attack hit with 100% chance) and Sheer Cold, giving it a guaranteed Two-Hit KO.
In Generation I, these moves always fail if the opponent has a higher Speed stat than the user. In later generations, this is changed so that instead they always fail against opponents of a higher level.
One particularly nasty implementation of the move Sheer Cold comes in the form of a glitch which enables you to make a Machop or its evolved forms learn the move. One of Machop's possible abilities is No Guard, which makes its attacks always hit at the expense of always being hit by opponents' attacks too. Do the math, and you get an instant KO which never misses. The reason Sheer Cold is preferred with this trick is because nothing is immune to Ice-type moves, and even a not-very-effective hit will be a guaranteed KO.
A Pokémon with full Hit Points holding a Focus Sash will survive a potentially OHKO move (even if it's a regular attack that deals a lot of damage and not an automatic KO move) with 1HP instead. The ability Sturdy also protects against automatic OHKO attacks — it was later modified to also work like a Focus Sash.
All of the aforementioned moves are also present in the Pokémon Mystery Dungeon series where they tend to be a lot more dangerous, due to only your team's leader needing to be defeated in order for you to lose. As a result, keeping Reviver Seeds on hand as a precaution is typically a wise idea when exploring any dungeons known to contain Pokemon with OHKO moves, as only the Sturdy ability will protect you from them.
These fall into the Awesome, but Impractical territory in the Pokémon Rumble series, as while accuracy isn't an issue, they have a ridiculously long start-up time and don't work on bosses. While they will work on the boss strength normal enemies in the Battle Royales, getting them off without being interrupted or KO'd is almost impossible due to the sheer number of enemies you face simultaneously.
The psynergy Condemn can instantly kill although rarely. The summon Charon has a chance to instantly kill. The Djinn Serac and Whorl may OHKO enemies and Gale will sometimes blow enemies off the map, but you won't get the experience. Obviously none of them work on most bosses and the chance for some is rather low. That doesn't stop Dullahan from instant killing you with Charon. In addition, certain weapons such as the Assassin Blade and the Crystal Rod had unleashes that had the potential to occasionally OHKO enemies, and they even worked on the bosses in the Suhulla Desert.
Menardi and Karst have the Death Scythe attack, which can do this. The Ice Queen's Icy Kiss attack can also oneshot someone in Dark Dawn, a bit of a wake-up call due to the lower level at which you encounter her. Skorpna-type monsters in the Grave Eclipse have a OHKO move called Drag Down.
While you have to whittle away half her HP first, Reid's Omega Seal becomes a One Hit Kill for optional Duel Boss Valkyrie in Tales of Eternia.
Also in Eternia, and given a callback in Tales of Vesperia (PS3), bringing the Dhaos cameo from Tales of Phantasia down to half and pulling off Indignation is an instant kill in homage to Phantasia. In Vesperia, doing this is the only way to unlock Indignation for Rita.
Instant kills also exist in the form of fatal strikes in Tales of Vesperia, though they only do this to normal enemies, and can only be triggered after depleting one of their fatal strike gauges through use of arts. In the PS3 version, Clint can use this on you if he or his allies land enough hits. Notable in that it'll still kill you even if you have the otherwise invincible level four Overlimit active.
Tales of Phantasia also had a set of instant-death spells for Arche (and a summon for Claus), each with a varying accuracy as well as those pesky urchins in Moria Gallery touching which simply kills your character (except Arche).
A multitude of artes in Tales of Graces and Tales of Xillia have a chance of causing instant death when they connect. The instant death just comes as an added perk, however, so using them against enemies that are immune to effect is still practical.
The PS2Transformers RPG had a minicon which gave you the headshot ability. OHKO to mooks, 3HKO to the Heavies.
Dragon Quest has the "Whack" spell which may cause instant death to an individual enemy. Its advance form "Thwack" can affect the whole group, but has a lower probability of working. Finally, there's Kathwack (or Max Defeat before retranslation), which is also group targeting, but has a higher rate of success.
Two toys in Guardian's Crusade, Draken which does damage equal to half current hit points to everyone, and Versius, which doubles all damage. Sure you take it too, but if you keep an odd number of hit points, the rounding will save you. Doesn't work on the final boss though.
If the Mystic Spider fought in Chapter 15 swallows Zael after trapping him with its spider web, it's all over. Swallowing another member of the party won't mean the end of the battle. And in any other battle, even the deadliest enemy attack will only knock characters down at most (the game has a life system that allows the fallen character to get up up to four times). It's made stranger by the fact that when you fight a Palette Swap of the same boss later, the same attack doesn't result in instant death and Zael can simply hack at its insides until it releases him.
Dagran's Limit Break ability, Death Sentence, kills a mook after a brief amount of time. Other mooks also has this spell, so if they use it against you or your party members, the heal circles will be the only way to abort the incoming doom.
Child Of Light gives such abilities to players, not enemies. Aurora's Light Ray spells have a 10% chance of outright killing a dark creature. Oengus' passive skill Kiss of Death gives all his attacks up to 20% chance of causing instant death. An "obliterated" status appears if the effects trigger, and it's also the only status effect that doesn't work on bosses.
By pressing the F1 button, you can do this to your opponent (Ctrl+F1 kills yourself). It doesn't work on everybody, though...
Every character in Guilty Gear has an "instant kill" technique. Land it and you win the round; miss, and your super bar disappears completely. This was even more egregious in the PS1 version; the setup for the instant kill was either punch+ kick or a well-timed block, there was no penalty for missing, and you won the entire match.
In Guilty Gear'sSpiritual SuccessorBlazBlue, Instant Kills have been replaced by Astral Heats, which seem to have been excessively nerfed. They can only be used in a tiebreaking final round of a match, require 100% of your super bar, and can only be used when the opponent is below 25%, at which point any normal super move would likely win anyway. After all, There Is No Kill Like Overkill. Continuum Shift seems to have un-nerfed them. You can now use them in round 2 of 3 if it would win the match for you, and your opponent can be at or below 35% health.
Persona 4 Arena features instant-kill attacks. The input for them is universal (down-down-down-C+D) and they require 100 SP to execute (a full meter of SP without Awakening). They are highly situational, though: they can only be used if winning the round would win the entire match, and are badly telegraphed. Nonetheless, like in Guilty Gear, landing it will win the round instantly. And in addition to their regular Instant Kills, the characters Naoto and Elizabeth have super moves which are one hit KO's if they hit. Again, these are highly situational.
The Home Run Bat item has this effect — landing a smash attack with it is an almost-guaranteed Home Run Hitter KO.
In Brawl, some Final Smashes consist of one powerful attack that is (nearly) guaranteed to KO anyone it hits. Zelda's, Marth's, and Captain Falcon's are prime examples. Assembling the three pieces of the Dragoon is also an instant KO, even if the target hasn't suffered any damage. Unless, of course, you miss.
Roy's fully charged B attack in Melee. Ike claims this ability in Brawl.
Ganondorf's up tilt is instantly lethal in Melee, and mostly lethal in Brawl.
The final boss of Subspace Emissary, Tabuu, has the infamous "Off Waves", three successive screen-covering attacks that will kill you if you don't dodge with absolute perfect timing.
Jigglypuff's Rest is capable of killing at 0% depending on the situation, but will usually one-hit KO anyone close to or above 40%. The price? The hitbox is pretty much confined to Jiggly's eyes, and if you aren't placed right the instant you use it, you've got 3 seconds to sit helplessly while your opponent charges up a smash. Also, even if you do get a kill, unless it's off the top, your opponent is going to come back to life before you wake up, which means they will kill you if you're above around 80%.
The "broken but balanced" hack Brawl Minus gives one to Ganondorf in an effort to make up for his place at the bottom of the tier list in the vanilla game. His slow Warlock Punch does 666% damage and knockback to match, sending enemies off-screen instantly.
This one-hit kill takes some work, but in the first SSB game, Fox's reflector will bounce a projectile back at its shooter for 1.5 times the damage and knockback. When it comes to reusable throwing items however, the damage increase can be stacked for each time it's bounced off the reflector. So when you use an item that's pretty powerful to begin with like a green shell, and have it thrown against Fox's reflector two times (computer AI opponents will happily do this for you), you suddenly have a "charged up" green shell of death that's powerful enough to KO another player even at 0% damage.
Little Mac has a power meter located just above his damage gauge that fills as he takes and inflicts damage. Once it's full, his neutral Smash turns into an uppercut that, in one single hit, will send anyone it hits flying into oblivion.
The Fist of the North Star fighting game for the Atomiswave and PlayStation 2 has the Deadly Fist Blows that works similar to the Instant Kill from Guilty Gear. They require a bit of build-up, however, as you must hit your opponent until the constellation under their lifebar is reduced to a single glowing star, which usually takes more than one round. This seems to be to ensure that when you use the Deadly Fist Blow, the entire match is over (not just the round). Since it's possible to combo into these, and they don't require any special stance (unlike the Instant Kills), which allow them to be used as surprise attacks, Deadly Fist Blows have seen use in Tournament Play, and many players consider finishing the opponent off with one to be a point of pride.
Igniz from had a move called "Brutal God Project" for his SDM where he pins your character back against the wall and unleashes his entire repertoire of (immensely high damage) attacks on you consecutively. It is, unsurprisingly, a 1-hit kill for the most part (Note that in this game: character stamina gets higher as you sideline more characters as strikers so a one man fighter with three strikers could theoretically survive "Brutal God Project" at full health). And he most commonly performs it as a follow up to his reversal special move which juggles. There's a reason that Igniz's portrait is at the top of the SNK Boss page.
Ralf's Galactica Phantom SDM/LDM in 97, 98, 99, 2000, and XI qualifies if it hits as a counter. In XI, though, it depends on the damage setting, as in who you're fighting. One of a team, yes. Single person, e.g. boss, no.
SoulCalibur IV also has these now, a first for the series. They're called "Critical Finishes" and they work in a similar way to Fatal KOs in Fist of the North Star. Constantly forcing an enemy to block powerful attacks, or Guard Impacting them around a lot, causes their Soul Gauge to turn from green to a flashing red. Once fully emptied, a single strong hit will send them into a vulnerable state ("Soul Crush"), and the Critical Finish can then be performed.
Time Killers was notorious for having this. A well-placed hit at any point in the round would instantly kill your opponent.
Kengo: Legend of the 9 (aka Kengo Zero in Japan and Europe) has a gameplay mechanic where your Stamina, although it can be depleted by many things (including walking), only itself affects one thing — whether or not that person can be one hit killed; basically one of the swordsmen initiates a Kumitachi (sword lock), the two attempt to physically overpower each other as they move around, draining Stamina, and one who loses all his Stamina is susceptible to, after being thrown, being one-hit killed.
Barbarian may well have had the first One Hit Kill in the history of one-on-one fighting games, and without being a gamebreaker to boot. You could use a decapitation move at any time in a fight (complete with a shower of badly pixelated blood), but the long buildup time made it very easy for the other player to dodge or interrupt.
Occasionally you will encounter gold manikins that have exactly one HP. Hitting one of them with an HP-damaging attack at any point in the match will result in instant victory. However, early on in the game, some of them will also have insanely high Bravery levels, meaning they can do this to you, as well.
The infamous Iai-strike Build, man. It kills the majority of things in simple two button presses: one to instantly Break your opponent, the other to execute the 9999 HP damage. Character HP naturally caps at 9999. Oh, and some characters' HP attack *cough*Yuna's pony laser*cough* also damage Bravery, potentially making it actual One Hit Kill. Feral Chaos suddenly looks trivial.
Paul Phoenix has a move called "Burning Fist" (Back+ both Punch buttons) which will not only take a second to charge up, but will take out the opponent in one hit (and send them flying backwards). Some YouTube videos show Paul playthroughs comprising of nothing BUT Burning Fists.
Jack has an attack called "Dark greeting". He takes a step forward, with sparks flying from him, and makes a quick chop downwards with his hand. If the opponent is in range, they're down. Ditto for the Wind-up Gigaton Punch.
Kuma's "Fatal Wind", which is extremely difficult to hit with.
Miguel in Tekken 6 has an unblockable move. He puts his hand over his mouth and laughs, then he winds up and punches the opponent. It's easy to stop him during the laugh or the wind-up, since they both take a while. But if he does manage to land the move, it's an instant K.O.
Headshots with a sniper rifle in pretty much every FPS will instantly kill it's target regardless of circumstances, unless it's a boss or invincible. Whether or not you can pull off headshots with other weapon varies, and if you can, it tends to be a damage multiplier rather than a guaranteed kill. This is so common and expected that it has its own trope.
Another staple variant in FPS is the Tele-Frag, which can be exploited as a valid means of killing in games like Unreal Tournament that have teleporting "weapons."
Golden Eye 1997 features the Golden Gun weapon, hindered by its one bullet magazine and that it only does enough damage to deplete either armor or health. There is also the cheat but equally devastating Gold Walther PPKPP7, which can kill anything in one shot, and has a 7 round magazine. The Golden Gun comes back in other James Bond games, and is something of Flanderization of the version of it in The Man with the Golden Gun. In the film, the bullets were no more damaging than regular bullets, it was simply that Scaramanga could always fatally shoot his targets in one shot. It had a one bullet magazine too.
In Urban Terror, a shot to the head with any weapon is a OHK, unless they have a helmet, in which case some weapons won't deal enough damage; even with a helmet, a sniper round to the head means death. The Remington sniper rifle is a OHK anywhere, except the arms, in which case it does "only" 67% damage.
This is subverted in the Jedi Knight series, where Force-sensitive enemies will dodge your sniper shots, even if they don't see you. Of course, this is because the lightsaber is the most powerful weapon in these games: one slash is usually enough to kill any non-Jedi enemy and one well-placed slash with the "Strong", Darth Vader-like style is enough to kill anyone except the bosses. Jedi Outcast also includes the hidden "realistic combat" mode, which unlocks the lightsaber's full decapitation and dismemberment potential, making each strike (even mere touch!) lethal. That also affects the enemies' lightsabers.
In Halo 2's Legendary difficulty, the Sniper Jackals kill you instantly no matter where they hit.
In the Syphon Filter series, headshots and explosions are guaranteed instant death for the player as well as enemies (except for certain bosses), regardless of armor and health levels.
In Combat Arms, the headshots were a one hit kill of course, but at one point, getting shot in a, ahem...sensitive region for males would also score a insta-kill, along with the humorous announcement "Nut Shot!" with a picture of two cracked walnuts. It was later nerfed to only occur when the fatal bullet (or melee attack) would nail the unfortunate player in the nads. Female characters could suffer this too, for balance reasons, but lacked the extra effects the males had.
Call of Duty 4 and beyond add a knife that is an instant kill if it connects. Bashing people with your gun in earlier games was also generally instant death, unless you did it with a pistol.
Some entries in the Unreal series include the InstaGib mod, which gives all players Shock Rifles with nearly unlimited ammo and each hit is lethal. This mode was available in Quake III: Arena, too, but with railguns.
Sort of with the headshots. Sniper Rifles would always be a one hit kill, and shotguns were a one hit kill in the head at close range (along with any other part of the body) but other small arms would just deal more damage than normal.
The RPGs in 2 and 2142 were one of the few weapons that would result in the victim not able to be revived by a medic, regardless on where they were hit.
And the Sniper's headshot ability, when fully charged, inflicts 450 damage,(and 518 with the Machina) exactly enough to kill an over-healed Heavy and (way) more than enough to kill anyone else.
On a technical level, only telefrags and falling into pits are One Hit Kills. However, the examples noted deal up to 500 damage without any modifiers and boil down to One Hit Kills except against a Spy using a the Dead Ringer or a Heavy affected by a stun during the time it gave victims a 50% damage reduction to make it less overpowered.
Sawblades, trains, and the Horseless Headless Horsemann deal damage equal to double your current health.
On the note of "so much damage that it's an instant kill, assuming there's no damage reduction," taunt kills. Taunting with a certain weapon out (it varies depending on the class) will make your character play through an animation that will kill any enemy unfortunate enough to walk in front of you at the wrong time. They do 500 damage, and as mentioned above, the normal maximum health count is 450. Most of these can destroy buildings instantly as well, whereas the backstab and headshot rely on Critical Hits to work, which don't affect buildings.
The Half-Zatoichi is a katana for the Soldier and Demoman. If you hit an enemy wielding one of his own with it, it does damage equal to three times his current health, causing an instant decapitation.
A cluster of well-placed stickybombs can also gib any player unfortunate enough to get caught in the detonation.
Getting caught right in front of a Heavy's minigun is essentially this; the thing deals insane damage at point-blank range (enough to shred even another Heavy in mere seconds). Of course, it suffers from damage falloff as range increases, but it has to be balanced somehow.
The demon morph Super Mode in Painkiller deals out one hit kills to mooks. Ostensibly, it's powerful enough to kill bosses in one hit as well, but with one exception (the final battle against Lucifer, a Puzzle Boss who is immune to your attacks) you can't get souls on boss levels, so no demon morph for you.
Counter-Strike features the infamous AWP (which, incidentally, isn't actually an AWP; it's an AW Super Magnum) which yields a one-hit kill no matter where the bullet hits its target.
The Farsight XR-20 railgun, which is like Counter-Strike's AWP, but even more broken. Not only can it instantly kill any unshielded target with one shot regardless of hit location, but it can also shoot through any number of solid objects. It gets worse, when you put the Farsight into its secondary mode it will also track the enemies for you, meaning the player could basically kill anything by pulling the trigger anywhere on the level. Broken indeed.
There's also the golden DY357-LX, a golden version of the normal revolver. It destroys anything that can be destroyed in one bullet.
Both the Farsight and the gold magnum have virtually unlimited penetration, so they would instantly kill as many people as you could get in a straight line.
The Crossbow has a secondary fire that turns it into a one hit kill weapon, which was far more useful than the primary fire, "Sedate". Add to that the fact that you could retrieve bolts if they missed, and you had a potentially infinite-ammo instant kill weapon.
The Tranquilizer Gun also has an instant kill function, although it ate up a lot of the gun's ammo and functioned as a melee attack.
Emissions in S.T.A.L.K.E.R.: Clear Sky and Call of Pripyat. They are one-hit kills, except in Call of Pripyat if you have Marked by the Zone achievement (Survive emission three times without taking cover, it's possible with special pills called Anabiotics) and enough health, but even then, it will leave you with just 2-3 bars of health, and you will pass out. More mundanely, headshots will kill most human enemies with one blow. The RPG and Gauss Gun take this to the next level; they will kill almost anything in one hit. Good luck finding ammunition, though.
Lighting common infected on fire in Left 4 Dead will kill them instantly. Direct impacts from explosions will also kill the small fry in one blast.
PAYDAY: The Heist has trip mines, small explosives that can kill any enemy instantly, including the heavily armored Bulldozers.
Devil May Cry has "Heaven & Hell" mode, in which every attack, player or enemy, is a one-hit-kill. It also has "Hell & Hell", in which only enemy attacks are.
Travis' Darkside Mode allows for one-hit-kills of a most violent degree.
Shinobu has a pair of near instant-death attacks after she Turns Red: she can take you from full health to two points with her supercharged Gengoken attack, and her multi-Sonic Sword attack will off you if she hits you with all the blades. And she is the third boss of the game.
Harvey Moisewitch Volodarskii and Bad Girl also have instant-death attacks, the former if you fail to break out of his magic box, and the latter if you fall for her trap. Henry breaks one out once his health reaches Turns Red territory; it's the one that looks like the Stinger from Devil May Cry and plants you into the concrete.
Surprisingly, there are fewer one-hit kills in the sequel, but they're noteworthy:
Captain Vladimir's extended Kill Sat laser and the final boss' violent defenestration attack. More frustrating is the latter, though, who is more or less a checklist of The Computer Is a Cheating Bastard, with teleporting, chaining attacks, ranged attacks, multiple forms, and possibly most frustrating, a OHKO that really can be ANY move, so long as you're on a specific third of the stage (or, if the attack is too strong, almost anywhere).
Travis gains another OHK in the sequel: turning into a tiger and ripping apart the suddenly-terrified enemies.
Kill Counters and Superstyle moves in Heavenly Sword. Kill Counters are performed by hitting Triangle as soon as an attack is blocked, Superstyle moves are performed by beating up enough enemies to fill your power gauge, then pressing Circle near an enemy. Superstyle moves are also used on some bosses, where doing so triggers a QTE that defeats the boss if performed successfully. Kai's arrows also kill most enemies in one or two hits, depending where on the body you hit them.
The Critical and Deflect Critical moves in Onimusha 3, though they are phenomenally hard to pull off. Once pulled off, though, you can chain them using the "Chain Critical" move (after learning it), allowing you to kill loads of enemies in one move. While in Onimusha mode, using either of these moves kills every enemy on the screen.
In Sengoku Basara, Shimazu Yoshihiro has a Super Skill that will kill any enemy in one hit, whether they be ordinary mooks, bosses or giant robots. Date Masamune's TESTAMENT, when charged for exactly 6 seconds, comes close.
For balance reasons the game initially didn't allow players to get these abilities. Doesn't stop some boss monsters, however. Even then, some monsters have abilities which kill them, but deal area damage based on their HP (Unless they have the Ninja job 2-hour, then nothing happens to them). Considering most of these mobs have thousands of HP, well, do the math.
An update added a playable an instant death ability in the form of the new avatar Odin, which will have AoE death (but with less accuracy the more mobs that surround it), on all normal mobs.
The Hard Mode version of The Great Wolf of the Air can fire its rocket launcher every other turn, which can only be reduced by pure Damage Reduction. In cast you were wondering, each rocket deals Your Max HP plus 50 damage on its first attack, and increases by 30 every turn. Combined with ML in the thousands plus a steep soft damage cap makes it a tough boss to take down without some preparations.
The Bomber-type B-Gears are walking One-Hit Kill (named OHKO by players in-game) dealers. The de facto B-Gear weapon, Bawoos, regularly deal 1000 HP damage per missile, while B-Gears are famous to be able to throw at least 6-8 of them forwards, and 12 or more downwards. Coupled with the fact that most Gears' HP range in around 6-7k HP total, OHKOs are frighteningly regular.
Another B-Gear example would be their Finishing Move, Big Boom. This move sacrifices one's own gear to take down others equal to its own Energy. With custom made Veils (armors), BBs can hit up to 14k damage, effectively acting as a very effective crowd-control move.
The game has most of its raid bosses set to an "enrage" timer that activates at the point the programmers determined to be most logical for the difficulty cap for the boss, upon which point the boss in question gains massive attack strength and attack speed, resulting in instant and rapid death for each member of the raid. Depending on the overall encounter conditions, the boss might be able to do this to the whole raid at once (Algalon uses Ascend To The Heavens to blow up the whole raid, Yogg-Saron extinguishes all life, kaput!)
The Lich King uses his Fury Of Frostmourne to wipe the whole raid near the end of the encounter, though the raid is resurrected shortly afterwards and wipes the floor with him.
Some boss abilities are basically avoidable One Hit Kills. Avoiding might mean to acquire an effect that protects against a good chunk of the damage, running behind line of sight obstacles, interrupting the spell or simply running away whenever it comes up. Tanks may or may not be tough enough to survive it regardless, but everyone else has to avoid it anyway. Some bosses even go as far as coupling this with getting stronger when they kill someone with such a spell.
Bloodlord Mandokir in the updated Zul'Gurub dungeon has Decapitate, which deals around 15 million damage to the target. It is unavoidable, and without a special ability like Cheat Death, it will one-shot anyone it hits. Fortunately, in this encounter death is even cheaper than usual in World of Warcraft; you can get resurrected once by each of the spirits around the arena, and only once all of them have done so or gotten eaten by the boss's skeletal raptor mount does death become like it usually is.
Additionally, it has become a standard tactic for any player that has a displacement/knockback effect (Elemental Shamans, Balance Druids, Fire Mages, and any particularly skilled Death Knight) to allow in their PvP strategy a means to place their opponent between them and a high cliff, causing instant death to anyone that doesn't have a means of slowing their descent (Mages/Priests respective 'Slow Fall' and 'Levitate' assuming they aren't an engineer with a parachute). You can also survive being thrown off a cliff with Warlock's 'Demonic Circle', although it requires good timing. Or simply use one of the Paladin's two Invulnerability spells and ignore the damage.
The Warriors Execute skill (and similar skills) is meant to be this, although usable only if the enemy is already at low health. Normal opponents and players will die (barring damage-preventing effects like the Cheat Death talent), but against a raid boss it only deals heavy damage.
The Warlock spell "Curse of Doom" wasn't specifically a One Hit Kill, but designed to have the potential. It does the most single-tick damage of any of the Warlock's spells, but takes a minute before the damage is applied. If the damage kills your opponent, it spawns a Doomguard demon. On lower-level creatures it can be a One Hit Kill, (if your squishy warlock can avoid being killed for 60 seconds) but once you reach boss-level it just does a whole lot of damage. It's since been changed to Bane of Doom which instead deals hefty damage every 15 seconds (not One Hit Kill tier, though).
Deathwing is a unique example in that his final attack is something that you've already suffered through- The Cataclysm. This is the closest thing an MMO can get to a Nonstandard Game Over, as letting him use it causes the screen to fade to black as you and everything else is utterly destroyed.
Monks have a variant of this, Touch Of Death which instantly deals the monk's max health in damage to an (NPC-only)enemy that has the same or less HP than the monk's maximum, effectively killing them instantly and ending the fight. For the Brewmaster, this means you can one-shot normal monsters, since, as the tank spec, they have a high max HP.
In the Assembly of Iron encounter, if Steelbreaker (the giant) is the last of the three alive, he will use an attack on his current target that gives a damage buff, but kills that player after a little while. As such, killing him last is typically considered the hardest way to do the fight.
In Throne of Thunder, if High Priestess Mar'li is empowered with Gara'jal the Spiritbinder's spirit, she summons Shadowed Loa Spirits that instantly kill their victims if they reach them (and leap over to them and kill them if not killed in 20 seconds).
A hefty chunk of the opponents players face in the Brawler's Guild are capable of this in one way or another, the main challenge being to avoid it while still managing to burn them down fast enough to beat the enrage timer(at which point the arena automatically One Hit Kills you with a rain of fire.
The right combination of buffs can grant these, though certain archetypes have an easier time doing it.
Blasters need only combine their Build Up, Aim, and Sniper attacks. Though it should be noted that this will only work against "minion" enemies, or "Lieutenants" who are lower level than the blaster in question.
Stalkers need only perform an Assassin attack while Hidden.
Scrappers can do this with a well-timed critical hit.
EverQuest has three player-usable insta-kill spells: Disintegrate (destroy target), Banishment (destroy summoned target), and Banishment of Shadows (destroy undead target). Usually regarded as Useless Useful Spells because they are often resisted, unusable on higher-level creatures, expensive to cast, and deny rewards for the kill.
World of Tanks has the Ammo Rack on each tank. It usually requires striking the tank from the side or behind, but it's a high value target as damaging it increases reload times and destroying it is an instant kill. The game even displays a special icon for ammo rack kills. Later versions have stated that the tank will not be killed by destroying the ammo rack, if it is not carrying any ammo.
The Unimatrix 0047 Command Ships, a group of ten Borg bosses, have a Plasma Energy Bolt attack that consists of a Painfully Slow Projectile. If it hits your ship it will usually disintegrate you even if you're at max HP and shields (you might survive if you built your ship as an uber-tank, but it's unlikely). Fortunately the projectile is also destructible, and its splash damage can be used against the ship that launched it. The player also has access to this attack if they use the bridge officer power "Torpedo: High Yield" on an Omega Plasma Torpedo Launcher, but theirs is much weaker.
The pair of Unimatrices in "Hive: Onslaught" also feature an energy lance in addition to the plasma energy bolt. You're supposed to be able to avoid it by staying near the Borg Tetrahedron containing the Borg Queen, but sometimes they bug out and lance you anyway. They may also bug out and lance you from 30 kilometers away, a range that is normally impossible to even select a ship at (most weapons will only fire at ten kilometers or less).
The assimilated IRW Valdore that appears as the boss of "Khitomer Vortex" is a Borgified version of the IRW Scimitar from Star Trek: Nemesis, featuring the dreadnought warbird's signature thalaron pulse attack. The assimilated Donatra in command of the Valdore loves to fire it right after decloaking, but fortunately it's fairly easy to get out of the way in time (it fires in a cone in front of her and she can't maneuver while charging it). Certain tank builds can also survive a direct hit.
In ground combat, being assimilated by a Borg drone is an insta-gib.
MapleStory has several moves that either kill instantly with a high cooldown or have a small chance to instant kill (the latter being nerfed in a patch that increases enemy hp hoping to encourage party play) in addition to just doing regular damage. Depending on how the move is coded, the instant kill will either do the target's max hp in damage or simply hit the damage cap. All bosses are immune to being instant killed, and all moves with instant kill as their only effect simply do very heavy damage to bosses instead.
The demonic black Smiles during the boss battle of the sixth chapter. In fact, six of the seven Smith members die inevitably because of them. Luckily, Garcian then grabs the ultra-powerful Golden Gun to kill the remaining Smile, as well as the boss himself, in one shot each. From there to the end of the game, he can kill with one shot any Smile (except the final boss, though it still goes down after five shots), without even having to aim at their weak points.
Sort-of-examples from the Dept Heaven series: Jihadnote Crusade in the English versions, Rivellionnote Angelic Thunder in the English versions, Judgment Zeronote provided only the unit head is alive, and Megiddo. While they don't immediately destroy the enemy unit, they are unblockable and result in an instant victory for the Clash they're used in. Jihad and Megiddo also come with damage bonuses.
Prince of Persia: The Sands of Time has an interesting variation. The ultimate sword kills any enemy in one hit, but you usually charge your time powers by stabbing stunned enemies with your secondary weapon, and there's no stunning when they turn to dust as soon as you touch them. But of course, by the time you get the ultimate sword, you've lost the Dagger of Time. So no harm, no foul.
The race against Metal Sonic in Sonic CD. Robotnik chases you with a laser- touch it and you're fried in an instant regardless of rings.
The Sky Canyon boss in Sonic Advance 2 has a hand-swat attack that will end you regardless of whether or not you have rings or a shield.
Some bosses in Sonic Rush have a one hit kill attack, too, but Eggman's generous enough to give you an audio cue ("Get ready to be schooled!").
In Act 2 of the Sonic Generations version of Seaside Hill, Sonic can run over the water by boosting. There is a giant chopper that attacks if you spend too long outside of certain areas. If it attacks, you lose a life, no matter what. Rings? Won't help you? Going as fast as you can? Won't help you. SUPER SONIC? IT'S NO USE!
Mega Man X2'sShoryuken kills any boss in one hit, provided you remain in contact with him long. Morph Moth is an exception as he pulls a One-Winged Angel in the middle of the battle. Curiously, so is Zero, by virtue of his ability to frickin' block your attacks.
Mega Man X3 downgrades Zero's Saber to a 2-hit kill, but it's still damn useful and a lot easier to get, especially since using it with the Buster upgrade causes it to fire out a crescent beam with the same effect.
Another "2-hit kill" attack is the upgraded Nova Strike in Mega Man X8. All Bosses fall to two hits (regardless of the health of the boss, the first hit always reduces the health to around 25% so the Boss could trigger its Desperation Attack). The previous incarnations of the Nova Strike is Game Breaker material enough, but this one?
If you've gone the alternate route in Mega Man X5(allowing Eurasia to crash & infect Zero), you'll have to fight Zero in his Awakened state as X in the final stages of the game. If 2 minutes have passed during the fight, he'll become invincible & repeatedly launch two large crescent beams at you (The attack is named "Genmurei"). One of the few ways to effectively dodge them is to use the Ultimate Armor's Nova Strike, but since you can't damage Zero at that point, the fight can only end one way.
No matter how many times, you can't defeat Wood Man? Have you tried hitting him with a full-power Atomic Fire after he drops his shield? As the link would attest, the whole goddamn thing's cyclic. (Two hits required in the Japanese version/America's "Difficult" mode.)
Like Wood Man, Metal Man has a weakness that will drop him in one hit outside the original Japanese version, except in this case, it's his own weapon. Sure, you can't do it until the second fight with him, but it's still damned funny.
Also, if aimed exactly right, the Air Shooter can hit Crash Man with all three tornadoes in one shot, killing him instantly. Even in the Japanese version, it will knock off over 60% of his life, making the next hit nearly a guaranteed kill.
In Iji, if General Tor's Eidolon gathers three charge orbs, he gets one of two attacks: If you've been using the Resonance Reflector, he'll fire a hail of nano to rip into you. If, on the other hand, you haven't figured out the trick, he'll prepare to fire the Phantom Hammer bunker-buster. This is signified by the orbs' dispersion and regathering into his gun barrel, and then he stomps the ground for a pull. If the seismic wave hits you or you stay in firing range too long, better luck next life. By the way, the Phantom Hammer doesn't just blast your health to 0 on a hit, it reduces all your stats to 0 at the same time. In terms of the story, this means that Tor's Phantom Hammer completely annihilates Iji's nanofield. With one hit.
This is the whole point behind WET's Golden Bullets mode. Every hit is an instant kill on a mook.
There is an enemy called Boss Bass that eats you in one gulp regardless of what powerup state you are in except for an invincibility star. A very annoying enemy indeed. Yoshi's Island has the Lunge Fish that acts similar to Boss Bass, except with a different pattern. As if that wasn't enough, both Lunge Fish and Boss Bass make an appearance in the DS sequel. The New Super Mario Bros. series has a Cheep Chomp that resembles a purple Boss Bass. It will try to eat you while you're underwater.
Super Mario 64: Swimming into Bubba's mouth or into a whirlpool, as well as getting crushed between a log and a hard place in Tall, Tall Mountain, trigger this.
Thwomps get upgraded to this in Super Mario Galaxy and its sequel; getting smooshed by one is fatal no matter how much health Mario has remaining.
Pouncers could one-shot Wario in the first Wario Land game, regardless of powerup state. Even if you merely bumped into its sides. This is because the sides and bottom were spiked, and spikes were an instant kill to Wario.
In the eighth level of the first game, the propellers in the lower end of the ship's stern can kill the characters instantly upon contact. They can only be disabled for a limited time, and it's the reason why getting the Jiggy behind them is called That One Sidequest.
Also in the first game, but in the last level, the eponymous characters play a quiz game. Failing to answer a question on the green-eyed skull tiles will send them to the lava automatically, and they will die.
In Banjo-Tooie, the sequel, the characters are crushed by a ton of iron if they lose during any of the three rounds of the Tower of Tragedy minigame.
In Conkers Bad Fur Day, some hazards and boss attacks are deadly if the eponymous character isn't equipped with something (i.e. being inside a tank or having a space suit). The propellers in the passage leading to the Uga Buga level, the rotating chainsaw from the Experiment, and the tail slash from the Alien are signature examples. The silver gun's shots, any Boom, Headshot hit, the chainsaw, and the katana blade all have this effect in multiplayer as well. The bazooka is this in both multi and story modes.
In Donkey Kong 64, some dark places house searchlights that try to illuminate your character. If it happens, you'll have one second to escape before a sniper rifle shot kills you instantly. Most of the time, death ensues.
Donkey Kong Country 3: In the level "Rocket Rush" if you impact the ground too quickly due to lack of fuel or simply neglecting to slow down your ship, then you instantly die even if you have both your Kong characters active. It's also the only instance in the DKC trilogy where you can see both Kongs' "death" animations at the same time.
In Castlevania: Order of Ecclesia, the Death Ring dramatically increases physical and magical power, but any hit will kill you. It's the best way to get Boss Medals, since you need to take no damage/take no hits to get them anyway.
In Mutant Mudds, there are swinging hammers on the fifth and final set of levels that will smash you into the foreground when they hit, instantly killing you.
In RosenkreuzStilette Freudenstachel, you get Kopiekreisel from Trauare, which, if used on Count Michael Zeppelin in the first Fortress stage, is guaranteed to land a 1-hit kill on it for sure. Then again, it works a lot like the Top Spin weapon from Mega Man 3.
In the last level of Tiny Toon Adventures: Buster's Hidden Treasure, just before the final battle with Montana Max and his robot, you have to outrun Elmyra Duff on your way to the boss room. If she manages to catch you, Buster will hold up a sign that says, TRY AGAIN, and you instantly lose a life. There's also the Spikes of Doom, especially in the Ice Mountain levels.
In contrast, the non-reflective lava later in the level doesn't instantly kill you if you fall in it (unless you're playing the game on Hard Mode, but that's another story), it just takes away a bit of your health.
Kid Icarus: Uprising has two enemies that can kill in one hit: the Tempura Wizard, who turns Pit into a piece of tempura-fried shrimp and chases him down to eat him, and the Orne, who can kill Pit just by touching him, and unlike the Tempura Wizard cannot be killed except in Chapter 9 with the Arrows of Light. To emphasize how deadly the Orne is, the game's music even changes to an ominous 8-bit tune.
Puzzle Quest 2: Two boss enemies (The Yeti and the Iron Giantnote not that one) have Crushing Kill, which deals 999 damage (more HP than all but the most dedicated level grinder will have). The final boss has Subjugation, which makes the player instantly surrender the fight, winning or losing.
In Joe Danger, the horizontal red bars will violently knock you off your bike anytime you make contact with them. NO. EXCEPTIONS. It doesn't matter how many times the game's liberal application of physics have allowed you to land in ways that are physically impossible for someone on a motorbike, if even the slightest part of you touches the bar, you are sent flying. While other objects in the game will also send you flying at the slightest touch, they tend to be more noticeably dangerous; nobody expects to survive landing on a spike strip or giant mouse trap. Other objects in the game are randomly given the same instant death property as the horizontal bars, but they exist in hard to reach areas as Insurmountable Waist Height Fences.
The "game ender", a unit or structure that can only be built at or near the end of the tech tree, and even then only at considerable time and expense, but once built, (almost) uncounterably devastates your opponent, is a staple of RTSes. Nuclear warheads are popular, but a recent trend is to include a mobile unit with a short to medium ranged weapon that can one-shot anything.
In Warcraft II, the Mage's Polymorph spell turned any unit into a neutral critter. Unlike in the sequels, the spell is permanent, making it work like a one hit KO.
Warcraft III has the Transmute spell used by the Goblin Alchemist hero, which can oneshot most non-hero units and convert them into gold for the player who owns the Alchemist. There's also the Doom spell by the Pitlord which deals damage over time until the unit dies, upon which a Doom Guard is spawned. There's also the Finger of Death spell used by various NPCs in the campaign that just seems to kill stuff outright.
In Starcraft, the Zerg Queen could oneshot any non-robotic, non-Archon ground unit with its Spawn Broodling ability. Also the Terran Science Vessel's Irradiate ability deals 250 damage over time to any organic unit, which is for all practical purposes a one-hit kill against nearly all organic units with the exception of the high-hp Ultralisk and Devourer, and the latter will be on the brink of death after being irradiated.
Electricity can kill the eponymous Pikmin instantly, so any enemy attack based on this element is lethal. Same with bombs and any other explosive attack. Good thing Yellow Pikmin can use bombs in the first game and resist electricity in the second.
Command & Conquer: Red Alert: The attack dog will one-hit kill any infantry unit. Not very notable most of the time since infantry is pretty weak to begin with, but some weird levels have these super-powered infantry that you might have trouble with but can be neutralized rather quickly with attack dogs.
Defense Of The Ancients All Stars: Axe's ultimate skill unconditionally kills any hero below a certain HP threshold, even through other skills that normally protect you from fatal damage.
Many, many games have ended with the message "Oh no, <monster>'s using the touch of death!" The player can sometimes acquire their own version of this spell, called Finger of Death, after the D&D spell listed above.
Not to mention being turned to stone, being transformed into a green slime, being disintegrated, being dragged underwater, being eaten (not instantly fatal to you, but fatal if done to/by pets), swords that can behead or bisect you or an enemy instantly, and of course the wand of death.
The canonical One Hit Kill and Yet Another Annoying Death is "You fall into a pit! You land on a set of sharp iron spikes! The spikes were poisoned! The poison was deadly...". Being on the wrong end of this is a sure sign that the Random Number God is out to get you, as it requires: firstly, that a spiked pit be generated; secondly, that you hit the chance that the spikes are poisoned (1 in 7 each time falling into the pit); and thirdly, that the poison is classified as deadly (1 in 20 chance each time you take poison damage). However this can be avoided through Acquired Poison Immunity.
Nethack has the concept of a "delayed instadeath" where whatever it is will kill you, but only after a few turns, allowing a lucky and knowledgeable player to save themselves. Examples include the Amulet of Strangulation, the above mentioned transformation into a green slime, and some instances of being petrified.
Shoot 'Em Ups
One of the starting weapons in ColourFire's arcade mode is a virus that infects enemies and kills them in one hit, blowing up into even more viruses. The only trouble is its short range, and that it has to wear down their health from the inside before they die.
Similar to the above is the Doomsday Infector from Bubble Tanks 2, except the range is infinite and the virus homes in onto the enemy.
Hisoutensoku has Reimu's Fantasy Heaven, which is so strong that if you use it in the third round of a match, it gets its very own theme music. The move is one big Shout-Out to the Hokuto no Ken example above; the theme music that plays in the third round version is suspiciously similar to the Fatal KO theme from the HnK fighting game, and the move is called "Musou Tensei" in Japanese, which is also the name of Hokuto Shinken's ultimate technique.
In Space Invaders Infinity Gene, the Classic weapon (modeled after the cannon's design from the original game) first a single laser that can kill any normal mook and most sub-bosses with a single shot. To keep this from being a total Game Breaker, the Classic cannon can never be upgraded, and is next-to-useless against the Final Boss.
"Romanov Attack Satellites" will fire out a deathray below that fries your tank instantly. To avoid death, keep firing at it to push it away so that it will not fire its laser while moving towards you.
"Shovak Bulldozers" are advancing mooks of doom that kill you if you brush against one. To avoid death, you have to push them away by constantly firing at them.
Any hit that results in a bisection is always lethal, as well as immersing a creature in liquid and then freezing the liquid (magma into obsidian or water into ice), or caving walls or floors in on an enemy. Other favourite, but less reliable kinds of instant death are magma (although some creatures are immune to it), dropping bridges on the enemy (except for the biggest creatures), and decapitation or piercing the brain with a weapon or shattered piece of skull (as long as the target isn't undead and has only one functioning head left, and has a functional head to begin with).
Some forms of evil weather, such as the ones found in Waterburned, are instantaneously fatal to dwarves.
The LBX/20 shotgun in MechWarrior Living Legends will one-hit-kill any jet fighter in the game if enough of its pellets hit the plane. The Long Tom Artillery Piece, carried by only one unit in the game, will one-hit-kill anything lighter than 50 tons with a direct hit, and near-misses will kill light mechs and hovercraft. While the LBX is horrendously effective versus other targets, the Long Tom suffers from a massive minimum rangenote unless the artillery tank is parked on a hill, it cannot aim low enough to hit anything within a hundred meters, a painfully slow reload time, a pathetically slow engine, and a total lack of support weapons.
In Nomad (a.k.a. Project Nomad), all space combat is done with missiles. The most powerful missiles are the Phelonese Quietus missiles capable of destroying any ship (except for 2) with a single hit. They're also the most expensive (relatively, as the trading system in the game is of the barter variety) and can only be purchased from the Phelonese. It should be noted, though, that the missiles alone don't guarantee victory in a battle. The victor is usually whoever has the best systems and faster reactions. You might have a dozen Quietus missiles, but the enemy has better targetting sensors and missile loaders, meaning he can put two missiles into your ship before you have a chance to fire your (slow-loading) Quietus missile.
In the X-Universe games, sufficiently powerful weapons can destroy certain ships in one hit. Scout craft, for example, will get vaporized by a single shot from a capital ship's guns, a single blast from any craft equipped with a Plasma Burst Generator, or certain powerful tracking missiles such as the Hurricane and the Disruptor. Earth's Torus Aeternal will vaporize any ship that strays out of the designated docking area - the Earth State doesn't mess around.
Helicopter and plane bullets are always one-hit kills in Wolf. Bullets fired by ground-based hunters may sometimes be one-hit kills, but are just as often two-hit kills.
Certain opponents in Punch-Out!! have special attacks that can knock Little Mac down instantly. Bald Bull, for example, has his powerful Bull Charge .... which can be countered to knock him down instead. Likewise for Mike Tyson/Mr. Dream's uppercuts. In fact, Little Mac can also knock down (or even out) his opponents during key circumstances.
Counter Attacks in Assassin's Creed I tend to result in some extremely brutal one-hit kills, i.e. slapping a guard in the face to spin him around and then stabbing your sword into his hip and out his crotch. Moreover, the assassin has full invincibility frames for the duration of the counter kill animation.
In Assassin's Creed II, while the archers, agiles, and regular guards with berets die in a single "counter kill," the regular guards with helmets have to have low health before this happens (counter attacks before that will only drain health as the Assassin drives them back), and brutes and seekers can only be countered by polearms, axes, or bastard swords (wielded by brutes, seekers, or mercenaries). However, in return for the smallest window of opportunity, Hidden Blade counters are always a OHK against any weapon, making it the best melee weapon for any player who can consistently time the button press, and the second game made it much easier to pull off, with fewer drawbacks.
In the later games, Sam can kill or knock out any guard he gets close enough to with a single quick and very efficient stab of his knife or punch/palm strike to the brain.
Conviction has the Mark and Execute system. Although you need to melee kill an enemy to make use of it, it allows you to mark up to four enemies and OHK all of them instantly (or fast enough that it doesn't matter).
The Tenchu franchise is based around stealth kills. If you attack a guard who is unaware of your presence, you kill him instantly and cinematically as only a freakin' Ninja can.
Hitman: The majority of Agent 47's attacks: strangling, poisoning, explosives and sniper shots, although, seeing as most of his opponents are mere humans, it's not surprising.
In the Thief series, human enemies can be instantly knocked out with the blackjack, instantly killed with the sword/dagger, or instantly killed with the broadhead arrows if shot in the head or chest. In order to do this, however, they mustn't be alert.
They must have been counting on players noticing the broken chain on either side of the fridge, which is fairly hard to see thanks to the graphics. The lesson there is to not attempt a no-saving run on your first playthrough. Oh, and Silent Hill 3 did have another of those One Hit Kill puzzles; remember what you do with the hair dryer?
Silent Hill 2's first encounters with Pyramid Head. Anyone paying the slightest amount of attention knows on sight that if that knife comes down on you, it's over. The first bosses of SH 1 and SH 3 also have instant-kill attacks.
The gamehas one hit kills on the common infected if they are set on fire. The sequel also supports this and also has incendiary bullets, making any gun similar to Golden Eye 1997's Golden Gun on the common infected. Shoving the back of a common infected while they are idle (just like Metal Gear) is an instant kill and is also an achievement. The sequel also introduces melee weapons, which can kill any zombie in a single strike (except Chargers, Tanks, and Witches), regardless of difficulty. The Magnum can also one shot common infected, regardless of difficulty or where you shot them.
Doing a Goomba Stomp to a common infected will also kill them instantly and break your fall.
Melee weapons in general can One-Hit Polykill the common infected, and one hit kill the majority of the special infected.
On Expert Level, the Witch only has to touch you to inflict a one hit kill. The Witch can also do this on any difficulty in Realism mode.
The earlier games had Neptune, who would swallow the player whole, the Hunters, who could decapitate the player, and Nemesis, who could impale his victims through the head, among others.
Capcom's Resident Evil 4 and Resident Evil 5 have various one-hit kills of two kinds, one from regular game-play or one from quick-time events. One-hit-kills during regular gameplay may result from the player-characters getting decapitated by enemies equipped with a chainsaw, impaled by a Garrador's Wolverine Claws, being crushed by a huge rock, or being eaten by creatures like mutated alligators (exclusive to RE5) or salamanders (Del Lago in RE 4). Failures for quick-time-events frequently result in deaths for the player characters.
Total Overdose gives Ram a variety of One Hit Kill options, but only the targeted headshot is worth any appreciable points. Most Loco Moves are instantly deadly in a pinch; the Tornado sprays dual uzis in 360 degrees, El Toro allows Ram to charge and headbutt enemies to death, the Explosive Pinata lures in enemies before detonating, and the Golden Gun is loaded with 4 bullets that autokill enemies in the general direction it's fired. These may seem like game breakers, but given the volume of enemies and increasing style-point requirements, their use isn't generally ideal, and mostly reserved for panic situations.
The Lancer assault rifle has an underbelly chainsaw capable of one-hit kills. Gears of War 2 however has an added quick-time event should two people lock themselves into a "chainsaw duel" and victory is achieved by the person mashing the melee button the fastest.
In both games, sniper rifle headshots, torque bow shot impalements, and Boomshot (grenade launcher) direct hits all are one hit kills.
In the third installment, there is the aptly named "One-Shot." Hit an enemy anywhere and he turns into chunky salsa.
Gotcha Force features several. The most potent is the Ultimate Cannon, which will one-shot anything that gets nailed by it. One of the harder stages in the game involves taking out six in a single level (which also features Arrow Ninjas that can anchor an opponent in place). Anyone nailed with a missile from the ICBM Tank or the Death ICBM also will get taken out in one shot, although those are easier to evade. These methods are distinct in that they are the one exception to friendly fire being Scratch Damage - friend or foe, these attacks will finish anyone hit by them.
While any enemy can potentially instantly kill you in Ghost Recon: Advanced Warfighter, the Hard difficulty boost their accuracy and has them always aim for the head, greatly increasing the chance.
Snipers and a few other enemies in Max Payne 3 can kill Max in one shot independently of the pain meter, which means you don't get a Last Stand even if you have painkillers.
The Immploder and Beam cutter from Desert Moon. The former instantly explodes a Mook and knocks back all mooks around it, while the latter fires a beam that kills everything it passes through. The downside of both weapons are the long intervals between shots.
In the first game, Chomper bites and all forms of one-shot plant, plus the Cob Cannon upgrade, can take out any zombie except a Gargantaur in one shot, usually several at a time. Spikeweeds inflict a one-hit kill on the Zomboni. On the zombie side, a blow from a Gargantaur's road sign, telephone pole or other zombie, or being run over by a Zomboni, will kill any plant except a Spikerock instantly. Dr Zomboss' attacks are also instantly lethal to plants, one of which is unavoidable.
The sequel has the Citron's Plant Food upgrade, which fires a plasma ball that bowls over zombies in its path and can even kill a Gargantuar in one hit. The zombies have the Explorer, who burns your plants with a torch, the Barrel Roller and Pianist, who run over your plants with a barrel and piano respectively, and the Gargantuar Prime who uses its Eye Beams to incinerate your back-row plants.
Mini Robot Wars has the Atomic Bot, which can instantly wreck anything short of a Giant. The upgrade allows it to even destroy a Giant in one hit, but not Titans. On the evil machines' side, we have the Giant and Titan which can both instakill a Minirobot in one hit, the latter can even destroy three in one blow!
The twin assassins Celia and Lede have an ability called "Stop Breath", in which they reach out to their target and do just that. It's 100% effective, unblockable (except via rarely-used items), and no, you never get to play with it yourself, because the villains always get the coolest toys.
One of the optional characters, Beowulf, has a petrification attack that works surprisingly often. Also, Cloud has an attack that kills, petrifies and/or stops his opponents. Not only is it his most reliably lethal attack (his other strong attacks, which simply do HP damage, are too slow to hit much of anything), it's also, surprisingly, one of the easier ones to obtain.
The Fire Emblem series has the recurring skill "Lethality", also known as "Silencer", learned appropriately enough by the Assassin class. It dispatches the foe instantly, even if a regular attack would have done no damage whatsoever.
In the Disgaea series, any attack that successfully hits somebody standing on a panel with the Deathblow geo effect results in instant death, regardless of whether the attack actually did damage. Also, in 2, the Samurai class has the ability to randomly score an instant kill with standard attacks while in critical health, and the Bone Dragons possess the Vendetta evility in 3 and 4, which allows for a low chance of an instant kill upon a successful counterattack.
Melee attacks in the Campaign mode of Transformers: War for Cybertron are a one hit kill (insert your own justification - Energon blades disrupting sparks or whatever). The downside is missing leaves you completely open, and actually getting into melee range is a dangerous prospect what with all the bullets and the Frickin' Laser Beams.
Next to flareguns, the lighthouse in the second DLC to Alan Wake, "The Writer", is this to the Taken when you're in an area that isn't obstructed by giant boulders (which can be "cleared" out).
Assassins from Monday Night Combat have some rather nastyBack Stab techniques with their bladed weapons. It's not strictly speaking a One Hit Kill, but the target's still helpless to do anything about it.
In Civilization, it can take a lot of time and trouble to conquer a city, and even more to destroy one. Unless you're playing Civilization: Call to Power and have an Eco Ranger unit; it will completely remove a city from the map in a single hit.
At the end of 2 trials in the third Ace Attorney game, Trials and Tribulations, you have to press the right statement/present the right evidence, or your ENTIRE life bar is wiped out. In the Japanese version, Godot calls this an "infinite penalty", while the English version calls it "the unlimited penalty". Justified by the fact that, when Godot threatens it, Phoenix's argument is based entirely on circumstance and conjecture, and failing to prove it shows that he most likely made it all up.
Fate/stay night had two examples. Lancer's Gae Bolg, the melee form of which would always strike the heart if he called its name (though he never really got the chance to do so). The stronger ranged form is technically blockable though Archer was the first to ever do so and could not continue fighting afterwards. Second, True Assassin's Noble Phantasm would automatically destroy the heart of his opponent, though it seemed to be fairly easy to avoid. If it DID hit you, you were dead though. Except Kotomine, who is immune to it due to the taint of Angra Mainyu. He still lived another two days after happening to have his heart destroyed anyway though.
There's also Bazett's ultimate move in the sequel Fate/hollow ataraxia, called the Fragarach. Being the ultimate counter to any enemy's most powerful attack (and only their most powerful attack, otherwise it's a worthless counter), it sends her Noble Phantasm flying into the opponent's heart before they make their attack. The problem with this move is that it functions in exactly the same way as Lancer's Gae Bolg, which also is magically designed to have pierced the target's heart before the attack is even made. Thus, if the two moves were used on each other, both fighters would be killed.
The RPG spinoff Fate/EXTRA gives us another example - The Assassin Li Shuwen's mastery over Chi and the fighting style of Ba Jiquan allows him to disrupt the energy flow of any opponent he strikes with a single touch, leading to his opponents dying after a single hit as their bodies ceases functioning. The technique is referred to in the game as 'No Second Strike' in reference to his historical boast that he never needed to hit an opponent a second time.
Shiki Tohno of Tsukihime has this as his defining characteristic: thanks to his ability to see "points and lines of death", get him within stabbing range of something and he will kill it with one blow, regardless of how powerful, tough, or "immortal" it is. This also applies to inanimate objects. Other than that ability, however, he is an ordinary, somewhat unathletic, and anemic high school boy, making him the ultimate Glass Cannon.
Probably based off the "Power Word: Kill" example in Dungeons & Dragons (see the Tabletop Games subpage), the Blade of Awe (usable from Bribing Your Way to Victory) in AdventureQuest has a small chance (0.1%) to instantly kill whatever you are fighting. There are dagger, spear, and staff variants of the same weapon with have the same ability, and dark and fire versions of the Blade of Awe which have a 0.12% chance instead.
You get to be on the receiving end: giants can smash you with their clubs so hard that you fly into the atmosphere, and dragons have an attack where they break your neck with their teeth if you're standing too close.
On the giving end, players favoring stealth and edged weapons can sneak up behind unsuspecting NPCs and cut their throats.
The first two Fallout games feature notorious examples of this trope. When scoring a critical hit on the head, eyes, or torso, you will, if lucky, land a hit that destroys the enemy immediately (and messily). This can lead to strange situations thanks to the game's damage mechanics: a character in full power armor might take zero damage from a critical hit, and then die instantly from the pain.
The M-920 Cain heavy weapon, informally known as a "nuke launcher." On Insanity it will still kill most enemies in one hit, in a very large blast radius, and it will probably kill you for the same reason. And it still won't do very much damage to the final boss, who (if you're really unfortunate) will be moving around too much for you to easily hit it anyway, especially considering that the final-boss area doesn't really have a whole lot of walls for you to just aim the Cain at and hope for splash damage. The Cain returns in 3, where Shepard kills an Anti-Air variant of the Reaper destroyer with it during the battle in London.
Thankfully Geth Rocket Troopers can't one-shot you on Insanity difficulty like they could in Mass Effect 1.
A level 4 Heavy Reave biotic attack can wipe out an enemy's health in one shot, although unlike most examples it will take a little bit of time for them to actually die.
Generic Husks, and to a lesser degree Abominations, are incredibly susceptible to directed force biotic attacks. A simple Push, Pull or Slam can wipe one out instantly, and a Shockwave can clean out entire groups in a few seconds.
The game introduces the Banshee, Phantom, and Brute, elite Reaper units capable of soaking tons of damage and dishing out just as much. All three have some form of instant-death attack that will end your game on the spot (although this only applies on harder difficulties). This is particularly aggravating in multiplayer, as the instant-death attacks prevent you from being able to be revived, which can end a game in very short order.
Cerberus Atlas Mechs can also do this, but it's so rare and easily dodge-able that most of the time you don't have to worry about it.
Unlike in Mass Effect 2, when introduced in the Retaliation Multiplayer DLC, Praetorians and Scions can also do perform similar moves.
"Priority: Tuchanka" and "Priority: Rannoch" each have a landed Reaper destroyer as the final boss, and in each case it has an attack that will one-shot Shepard: being stepped on in the first case, or taking a hit from the main cannon in the second. Justified, considering they're 160-meter light capital ships.
ME3 also introduces the Grab, where you pop out from behind cover, grab a nearby enemy, and stab/pound them in the face. Only Armored troops (and the Phantoms) can avoid being killed by the attack (you used to be able to do this to Geth Pyros, but that's been taken out). It's a bit situational, but there are multiplayer levels where you can funnel them in such a way that it's almost like they're waiting in line for you to pull them over and smash their faces in.
Origins gives Mages the spell "Mana Clash," which will instantly kill any enemy Mage or demon of less than Boss level (and some of the Bosses, if cast with boosted Spellpower). And it's an area of effect attack, too, so you can clear out whole rooms full of enemies.
Melee Warriors in Dragon Age: Origins – Awakening can learn a move called "Peon's Plight", which is an instant kill against generic mooks, does a double Critical Hit against elites, and a normal critical against bosses. Very useful for thinning out the herd, and an absurdly easy way to get the "Heavy Hitter" achievement (main character does 250+ damage with one attack).
Alex's defining move as it's OHK - eating people. The simple grab and Consume move will kill any normal military or infected enemy, and heal you in the process! Not so for the hunters, though, which need to be weakened before consumption.
A fully-charged Blade Air Slice is a One Hit Kill for just about anything but hunters, and his devastator moves are OHK for everything in the area of effect.
In Saints Row 2 you can grab anyone within melee range into a headlock, then hold them as a meat-shield or deliver an instant execution. (Or you could let them go, but where's the fun in that?)
In Red Dead Redemption, the two sniper rifles will usually kill any mook in one hit if its in the head or chest area. Also a headshot with any gun will do this too. Not to mention the throwing weapons always kill whatever they hit.
Multiplayer-spawned cougars can also inflict this on unwary players.