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That One Attack
A particular attack in an enemy's arsenal which is significantly more dangerous than most of its attacks.
If you have a party, it will almost always target all party members, and it often takes off the majority of your hit points, if not worse. It's a staple for That One Boss to have one of these, possibly more.
This attack showing up even once is always bad news; if the A.I. Roulette gives you two in a row, expect to see the Game Over screen. Whether or not you can beat That One Boss that uses this attack usually depends entirely on whether or not you can avoid/endure/recover from it.
Skill Gate Characters may also derive their harmful-to-newbies nature from having one of these, and thus falter when the opponent learns to counter it. If these are available to players without suffering Redemption Demotion, they usually become Game Breakers.
Butterfly Storm from Persona's Pandora. Large damage and status ailments.
Terror Fortune from Persona 2's Metal Jun. See above.
Bloody Divorce from Metal Eikichi: Huge Water Damage, and high chance of instant death.
Hula of Misfortune: Watch a hula-dance, lose half of your total money. You don't get it back.
Aimed Shot: Chance of instant death. One boss battle has his four elite mooks spam this on end.
Kudan's attack "Prophecy" kills the monster in question, but it will revert all of your active Personae to Rank 1 and remove any mutations they received. And it doesn't wear off.
In Innocent Sin: Mephistophiles. Random statuses to your entire party. And it's the opening move of a Chest Monster.
Night Queen from Persona 3's Nyx Avatar. Sizeable damage, devastating status ailments. If it happens to Charm your healer, get ready to fight the last form from the beginning.
On the other hand, if it happens to charm someone else, don't be surprised if the last vestiges of thine HP are wiped by any of many fun weapons.
On the same boss: "Moonless Gown." Not an attack, per se, but brutally unfair nonetheless. Not only does it make it entirely immune to damage (even almighty damage) for a couple turns, it also reflects that same damage back to you. The final boss of Persona 3 is a monster.
Not to mention that, in a truly irritating display of Artificial Stupidity, your allies will blindly attack the Moonless Gown unless you stop them, even though both Fuuka and common sense say that they shouldn't. This can be especially brutal if you've had to revive any of your allies, in which case they take their turn before you do.
The obvious answer to the above is to use your teammates that are immune to the same elemental spells that they cast, right? Wait, no, the boss just uses the appropriate Break skill to remove their immunity. And you thought you were so clever.
The Mythical Gigas' Deathbound hits everyone for a huge amount of Strike damage. It's about 300 damage if it doesn't critical (you'll probably have 480 HP, tops, by the time you reach him), and if it criticals, that number can easily exceed 1000, and no amount of Level Grinding will allow you to survive when that happens.
Elizabeth's infamous 9999 damage Megidolaon (the HP cap is 999, by the way.) She uses it once per move cycle, meaning you better have a way to counter it. And even if you do, if you break the rules of the fight, she'll immediately use it twice in a row to make sure you stay dead. The attack is so infamous that it returns in Persona 4 Arena as her One-Hit Kill attack.
Dark Embrace from Persona 3 FES's Erebus. When it uses this attack, unless you manage to deal enough damage in time, it'll deal a good amount of damage to you. Survivable at first, but it gets stronger throughout the battle, so when you see it charge up Dark Embrace, throw everything you have at it.
Izanami-no-Okami from Persona 4 has World's End, which is game-ending if you can't figure out how to avoid it. Huge damage to your entire party, chance of status ailments to everyone. She also follows it up by immediately using Summons to Yomi, which kills any character with status ailments. But it's only That One Attack to players that don't recognize when the game is telling them to defend: she spends her two turns charging up and telegraphing the attack the round before she uses World's End, and it does nothing whatsoever to characters who are guarding.
Rampage, used by the Contrarian King. Hits your whole party up to 3 times for huge damage and will one shot your entire party if you fight him as soon as you can.
Kunino-Sagiri's Control, which brainwashes one of your characters. They do the same things as they would if they were Charmed, but 1: it's unavoidable, and 2: it's incurable; you have to wait it out. After Kunino Turns Red, he'll take control of three of them. Just pray they don't use Diarahan.
Stagnant Air increases everyone's susceptibility to ailments by at least 50%, which then makes the combo of Evil Smile (whole party, causes Fear) and Ghastly Wail (anyone with Fear dies) a Total Party Kill unless you're really lucky. There are two Hope Spots to it, though; it can be used against enemies, and it wears off after a while.
Shadow Yukiko's Burn To Ashes for beginners. At this point, you only have three party members; one of which has a fire weakness. You can pick up a Slime that has Red Wall, which can seal said party member's weakness for 3 turns... but Slime itself is weak to fire, and the only healing spell you're likely to have at this point is Dia or Media. And since this is an Atlus game, the AI will exploit any chance you give it to murder you.
On the same boss, the Charming Prince has an attack called Terror Voice, inflicting Fear upon you. It's not so bad on its own. The real kicker is when Shadow Yukiko follows up with Shivering Rondo, which does a HUGE amount of damage to anyone inflicted with said ailment.
Everything used by Mitsuo The Hero. His regular attack can deal out triple-digit damage, is unblockable, and is enough to kill anyone in two shots, which is a serious problem considering Mitsuo gets 2 turns. Then there's Bomb, which deals massive damage and can cause Exhaustion, which drains SP every turn. Lastly, he has Gigadyne, which is as strong as his regular attack and it hits the whole party.
Shadow Kanji's Roar of Wrath, which gives female characters the Rage status. While this could work in your favor (when enraged, people will attack enemies with boosted strength), the only two females in the party at the time are Chie and Yukiko. And Yukiko is the designated healer for the party. He also likes to follow this up with Tetrakarn, making those powerful attacks go right back at the girls. Have fun watching them get instantly killed for attacking Kanji! This is also made potentially worse if you haven't killed off one of the flunkies that are HEALED by physical attacks.
Megidoladyne from Devil Survivor's Lucifer. Deals enormous damage to everyone in every friendly party, and gets stronger the more times he uses it. 50% more powerful, to be exact. Once he Turns Red, he will use it every turn. Lucifer will use it upon changing into his second form and every turn afterward. And inevitably again upon turning into his third form. Since Megidoladyne becomes more powerful every time he uses it, it becomes an instant kill on the entire map after four-five uses. If the party is adequately overleveled. Which means that you have to beat Lucifer's second and third form without letting him have more than two turns. Welcome to hell.
For reasons mentioned above, the fight with Lucifer can become literally impossible, as he will be doing more damage in one attack than the maximum HP any member of your party is allowed to have, regardless of level, and Lucifer is not capped on how often or how fast he can cast it. Lucifer is easily capable of casting Megidoladyne extremely rapidly in his third form at random, and even at maximum level with the best demons and skills possible equipped, making it so that no matter what you do to prepare, the fight with Lucifer has a real chance of being totally impossible to win after you've already beaten his first two forms. Welcome to hell, indeed.
Digital Devil Saga's Bonus Boss, Hito-Shura/the Demi-Fiend, gives us "Gaea Rage." Deals around 7,000 points of damage to every character when your maximum HP is 999. Not to mention the only defense against it is very vague and requires luck to work. You'll have nightmares about it. Additionally, he'll immediately throw it out at the start of battle if you have any elemental immunities, killing you before the command menu even shows up.
Being possibly the hardest boss in video game history, all of his attacks are pretty devastating. Javelin Rain hits everyone for decent damage and can inflict Stun while Xeros-Beat substitutes the (more devastating) Mute for Stun. Even his basic physical attacks are cringe-worthy, as not only do they hurt badly, but he has an ungodly high chance of getting a critical hit and getting an extra turn.
Adding insult to injury is having played Nocturne and realizing that Gaea Rage isn't even a particularly good attack. Apparently, he deems you unworthy of wasting Spiral Viper or Freikugel... or of bringing Dante as backup. He's generally not wrong about that.
There's also Vanity, the DDS equivalent of Bad Breath (see below).
Zotzilaha Bane, used by Camazotz. It turns one party member into a bat, giving them abysmal stats and a large weakness to Force. Three guesses what all of his elemental attacks are.
Matador's Red Capote maximizes his Hit/Evasion rates, making it nigh impossible to land an attack if you aren't prepared to counter it somehow.
Also, Andalucia, which hits the entire party several times. It doesn't do that much damage on its own, but is usually used after Focus, making the first hits very strong, or even worse Taunt, which puts a huge dent in your defense.
Ahriman's Apocalypse deals incredibly high unblockable damage. Pray that he doesn't use Megidolaon on the same turn.
If the True Final Boss ever decided to use High King or Root of Evil twice in a row, you were pretty much dead. Keeping your HP maxed every round was necessary to survive it, despite its low probability.
Dragon's Eye, turning one press turn into four halves.
Beast Eye, turning one into two halves. However, these halves can be turned into two more halves each. WHY?!?
Bael's Bane, which turns your ally into a fly. Can be blocked, at the cost of being weak to instant kill magic the boss uses (bar Crazy Preparation of course).
Death Flies: either you're immune to dark-type death or you... well, die. Otherwise you take heavy almighty damage.
Fire of Sinai: the random number generator god seems to enjoy having multiple hits of almighty on your main character.
Holy Melody if you're not careful. Yay, let's have the boss fully heal himself shall we?
Same goes for Evil Melody. Main character a bit lower on HP than other party members? HE DIES!
Anything used by Dante. Stinger hits one character for Almighty damage, and instantly kills anything on a Critical. Provoke is an enhanced version of Taunt, which drastically increases your attack but lowers your defense; Provoke does this and, instead of spending a huge amount of MP, it actually heals Dante's MP. He also has an attack called Showtime, which deals a gigantic amount of Almighty damage to your party, and Bullet-Time, which hits your party for pretty good damage and causes Panic.
There's also Rebellion, which has a crit chance so absurdly high that you might as well just assume it will always score a Critical Hit. And E & I which, although not as strong as other attacks, hits 4 times, so if he scores a Critical Hit with this, you're probably dead.
White Rider's God's Arrow: 100% One-Hit Kill if you don't null expel. It doesn't help that the same boss also has Prominence, the strongest fire spell in the game, so if you want to avoid one you cannot avoid the other.
Red Rider's Terrorblade. It does huge damage and can randomly cause the Panic status. One of three things will happen when someone has this status (aside from nothing): They lose a turn, they throw away some money, or if it's a demon, they might run away. Granted, you can call them back, but that's only if the Demi-Fiend didn't get hit by it as well.
Surt's Ragnarok. Good luck surviving that if you don't resist Fire. It doesn't help that later when he turns into a Degraded Boss, Surt appears in groups of at least 3, so there's a chance they'll use it more than once on the same target. You'd be surprised by the amount of times they do this to the Demi-Fiend....
First off, anything that causes fear. Your demons may not do anything — or even retreat — and it can last multiple turns.
Asura Roga, used by (who else?) Asura (and the final boss, if you're really unlucky). This causes Rage, which cannot be cured with anything but Amrita or Salvation (and you don't have the latter at this point). Rage is similar to Charm, with the minor difference that the victim can attack anything, Asura included — but the odds are much higher they'll attack the party.
Wave of Death, which deals ungodly damage. If Ouroboros uses it twice in a row, you lose.
Ouroboros also has another godawful attack: Disaster Cycle, which inflicts random status effects on everyone in the party. One unlucky turn where she hits the player character with Petrify or Bomb and you lose instantly. And in her second form, she spams it.
Any Almighty skill. You have no way to block them. (Neither do your enemies, but guess who'll face them more often?) Bonus points to Hostile Terror, this game's answer to Bad Breath (see below).
And finally healing ones: Tiamat, Captain Jack, and Ryan would be WAY easier if they didn't have Pure Blue to fully heal them and cancel all debuffs. Only Tiamat gives a way to avoid it (do not reduce any of her stats to -4). Or Commander Gore's Self-Denial, which heals and boosts attack, or that moment when he hits 0 hp and then regenerates 7500 spontaneously, giving a higher total HP than anything else in the game! This is a Nintendo Hard game, if not more so.
Speaking of Gore, Adaptation. This is an attack he will only use on the main character, and the only way to survive it is to have full health, be on defense, and have something equipped to resist physical attacks. Even then, there's no guarantee this move won't flat-out kill you.
And, depending of the amount of money you happen to have at hand, you will want to kill yourself if a an irredeemably stupid enemy hits you with Macca Beam, or God forbid, Wastrel Beam. You lose, not a fixed amount, but a percentage of your total. You can lose hundreds of thousands of Macca to Kangiten's Wastrel Beam.
Mother's Kiss, used by the Final Boss on the Law and Neutral paths. It hits 6 to 8 times for physical damage and can deal four-digit damage even with your defense capped. There is one way to negate it, but by using it, you make yourself vulnerable to the boss's One-Hit Kill moves. And she uses it a lot.
MA. Like Mitra's Light of Order, it is a guaranteed, unblockable instant kill of one character. This time, however, it CAN target the protagonist. I hope you know how to repair a DS.
The Balrog has two, but they're really two shades of the same attack: Pillar of Wrath and Scorching Inferno. Both of them hit every member of your party, and both will drain almost all of the AP your characters have.
Stomp from the Műmakil. Hits everybody, and stuns them. Stand Fast makes it mostly worthless (it's still kinda painful), but if it gets it off before Berethor gets a turn... Well, you're screwed.
The Final Boss, Sauron, has 2. Darkest Fear immobilizes one of your guys and deals damage over time, and Berethor's Immune to Fear Passive ability and Shield of Courage Leadership do not work to stop it, unlike regular Fear. Silence of Light also immobilizes your entire party's Spirit skills. It's a huge pain, since most of your best abilities are Spirit, and you need them to last long enough to kill him.
Cruel Ruin and Djinn Storm from Golden Sun: The Lost Age's Doom Dragon.
Literally every attack done by Dullahan counts as That One Attack. Dark Dawn might have been disappointingly easy, but Dullahan somehow got even harder.
Djinn Blast is a lesser cousin, but no less aggravating. Used by the Chaos Chimera in Dark Dawn and by Karthas in The Lost Age.
The fangame Touhou Labyrinth borrowed Djinn Storm, and it is every bit as annoying (Empties all party members' SP, including the SP of those in reserve).
The Chaos Chimera has Retribution, a reasonably strong attack which hits the entire party. It also has a chance of causing instant death. Oh, and the Chaos Chimera always attacks three times in a row. Have fun.
Star Magician used Mystic Call! Star Magician summoned Refresh Ball! Star Magician used Mystic Call! Star Magicican summoned Gaurdian Ball! Player's anger was increased by 259 points! context Refresh Balls heal the Star Magician to the tune of 1000 HP per cast, while Guardian Balls vastly reduce the damage he takes.
Ghoul Ball used Consume Djinn! Sveta's Fleet was eaten! Player's anger increased by 100! context Ghoul Balls, summoned by the aforementioned Star Magician, can lock one Djinn into Recovery mode (cannot unleash, convey stat or class bonuses, or use in summons) per invocation until the offending Ghoul Ball is destroyed.
In Valkyrie Profile, any enemy with the Great Magic spells will have it as its That One Attack, such as Akhetamen's Seraphic Law, Wraith's Gravity Blessing, Barbarossa's Calamity Blast, etc.
Almost every attack Bloodbane has qualifies. He will often follow up a damaging claw swipe ("I'll crush you!") with Feel My Flame, which deals huge damage to the entire party. Occasionally he will follow this with a magic spell like Sacred Javelin, most likely killing one of your Einherjar. And when taken down to below half HP, he will start spamming the Great Magic Gravity Blessing, which can cause a Total Party Kill.
Fenrir in the A Ending has Frost Bait, which it uses when at low health and deals huge damage with a chance of freezing anyone hit. A special item from the mid-game can stop it from freezing your party members, but it won't do much against the damage. The Fenrir clone in the Seraphic Gate, Carnage Beast, can use Frost Bait both at full health and low health. Encountering two Carnage Beasts and having them do two Frost Baits in a row is likely to result a Total Party Kill unless you have the Guts/Auto-Item/Union Plume combo.
The True Final Boss, Loki, has two: Extension Force, which deals a single devastating blow to each party member; and Dragon Orb, a unique Great Magic that is just as painful as the rest.
The Hamsters in the Seraphic Gate have Furry One, which tramples the party under a wave of hamsters for ludicrous damage.
In Digimon World 3, even some normal attacks are that one attack. Mamemon's normal attack can freeze your Digimon, with a very high chance of blocking it from doing anything. Even better: it blocks you from healing your Digimon. Depending on your luck, you'll just mash X until your Digimon die.
Hi Andromon has Atomic Ray, which has a solid chance of causing death regardless of your defenses.
Pharaohmon, the very first boss, has Necro Mist, a move that not only deals high damage, it also has a almost sure chance to poison your Digimon. Wouldn't be so bad if Poison didn't eat 25% of your HP every time you get a turn.
Vademon has an attack that has a good chance of putting your Digimon to sleep. Unlike in Pokemon, sleep makes it pretty much impossible to escape and definitely impossible to attack, making your Digimon a sitting duck for Vademon.
There's also Persiamon, used by the Game Master, whose special attack, Helter Skelter, dedigivolves your Digimon to its Rookie form, harshly slashing your stats. You can re-digivolve to that form immediately afterward, but good luck getting an attack in before Persiamon uses it again.
Digimon World Dawn Dusk has Chrono Destroyer, only useable by the final boss. High Dark damage, plus it can easily put your whole party to sleep.
Royal Slash is a Holy attack so strong that, in the more active era of the metagame, any player with more than one digimon with the move would be disqualified.
Especially if the enemy can attack more than once in a single turn, which by the second half of the game, most of them can! First turn, Disruptive Wave = Goodbye all defense and power boosts. Second turn, you get hit with an ungodly powerful attack. Have fun getting around that.
Corvus's Magic Burst in IX. Nothing more needs to be said.
Palaxius has a lot of cringe-worthy attacks, but Crimson Split stands out. It can easily deal up to 300 to every character (which will most likely kill any character except for Felt and Gray) and once he casts it, it sticks around on the time bar to come up at least four more times while he keeps pounding you. Did I mention he's lightning fast and his other main attacks hit for even more damage? Luckily, Crimson Moon and Shadow Azoth are can only target one character.
Ragu O Ragla's Volcanic Bomb in the first game, which deals 7000+ fire damage to all party members and is pretty much unsurvivable without absolutely insane amounts of grinding. The only other ways to withstand it is to make sure at least Cecilia is always equipped with a Goat Doll, or find Frog Badges, which nullify elemental damage.
In every Kingdom Hearts game, Riku has an attack entitled Dark Aura, wherein he'll become invincible and fly in quick dashes at your character. It does heavy damage and is very hard to dodge. It's even more devastating in Chain of Memories, although you do have 0 cards that can break it. It also helps that in Reverse/Rebirth you can use it yourselfasRiku. Also, Ansem's ultimate attack in Riku's last battle with him will almost certainly be fatal unless you dodge it.
Bonus BossSephiroth's "Heartless Angel" attack, which drains all of your HP and MP in one shot. If you aren't able to interrupt it, you need the ability that lets you survive lethal blows with 1 HP (Most people assume it's a HP To One attack because they haven't turned Second Chance off since they first got it way back in the beginning), but then you still have no MP to heal with. Ouch.
Though you can turn it around with items, if you notice him beginning the move's rather long start up and either acknowledge you can't stop him in time or are already quite low, you can activate a healing item. Because there's an uninterruptable delay between using an item and receiving the benefits, you'll take the hit sure, but surviving is easy and you'll be quickly restored (to full even if you choose) just after.
The second game gives Sephiroth an opening move that you have to block with an Action Command, otherwise you pretty much die. At least you don't lose that much progress if you mess up...
Xaldin's Wind Dragon in the Kingdom Hearts II. Multi-hit so it gets around Second Chance, does high damage, and is nigh-unavoidable. Thankfully, Reflega works perfectly well to shield you from it.
Birth by Sleep has the nameless optional bossthat the Japanese didn't get. This boss has Collision Magnet. Basically, the boss hauls you in with a rope and deals damage in mid air. First, it hurts. You need to be at a high level for this attack to not instantly bring you to your final Hit Point. Second, it's very fast and difficult to see coming, and unblockable. Third, it leaves you open for another attack, which can kill you if the rope managed to get you to one HP, without you being able to recover; even if you have Once More, because apparently the next attack, which you don't have enough time to recover for, counts as a separate combo. Your chance of victory is pretty much inversely proportional to how many times this boss decides to use this attack. This move was so bad that when the Japanese got their inevitable Final Mix, they nerfed this move to allow you enough time to dodge or heal, mainly to make the two new bonus bosses look challenging next to him.
AKA the "Rape Rope." It's telling that the tracking for it is so good that if you use or spam your dash/dodge move (which has invincibility frames and moves you very quickly), the rope will just latch on your character as s/he's dodging continuously for several seconds if you're able to keep it up for that long, so that it grabs you as soon as you run out of invincibility frames.
A lot of bosses in this game have some kind of inescapable stun-lock combo that in proud or critical difficulty will leave you with little to no health, requiring Second Chance/Once More and some form of healing ready. To make matters worse, HP isn't given by leveling up but instead is based on story events or through the HP up ability, and getting the latter can be a "Luck-Based Mission" or require grinding through an optional area. Leveling doesn't really help your survivability because defense is pretty negligible in the higher difficulties and you even get less than the standard or easy difficulty. Some bosses with combos like this: Terranort, Master Eraqus, Zack Fair, Braig, Vanitas, the Deep Space Boss, etc.
The Armor of the Master and No Heart from the final mix of Birth by Sleep each have their own. Aot M has a 20 hit combo almost guaranteed to reduce your HP to one normally, but if he's been allowed to enter his Super Mode by sapping you with his chain, it's a guaranteed kill. No Heart has his own variant of Heartless Angel late in his battle. It's uninterruptible but can be avoided, but if you either fall into one of his slow traps or are right next to him when he rises into the air, you will be hit. This is also a guaranteed kill if he uses it twice, unless you have an item which you'll likely have used up by then.
Ever wonder why everyone hates Terranort so much? Because he has a really annoying combo that stun-locks you and takes away most of your health, and even has two non-consecutive blows that can bypassSecond Chance/Once More if your HP was already depleted to one by then. It's the same combo that Terra uses himself when in Dark Impulse mode, but unlike Terra, he can pull this combo off at will, and this makes it very hard to hit him. He also has Ars Solum. How is it different than Terra's version of it? Well, it's unblockable, it is difficult to knock him out of it, and he can use it up to THREE TIMES IN A ROW. Of course, when you use it, he just blocks the first hit of it, and Counter Hammers you.
In addition, Zack performs Omnislash. You may feel pity for those hordes of enemies you murdered like that. It's used at the start of the battle, and can be used again during the battle. You are given a clue that tells you it's coming, and it's STILL hard to dodge.
The optional boss from Kingdom Hearts 358 Days Over 2, the Dust Flier, has an entire arsenal of these. First, there's a shockwave that will deal a random status ailment, a bombardment attack that comes fast and knocks you around like a ragdoll, AND the charge attack. The charge hits like three Mack trucks slamming into you one after the other. Glide makes it much easier to dodge, but you still have to deal with the Flier's ludicrous HP count. If you can bring down this airborne bastard, you've earned the right to trash talk.
The Mimic Master's laser attack in Birth by Sleep. He fires off two lasers, one bright and the other dark. If the dark one hits you, your field of vision is reduced and you lose the ability to lock on (as well as your Shotlock). It's also floor-level, so you need to jump over it and hope the bright laser doesn't catch you (although that just deals damage). Trying to run away from it? Don't bother, it takes up just about the entire field! And the Master is invincible for the duration of the attack.
Lest not forget Bonus BossKurt Zisa from Kingdom Hearts and his infamous Silencega technique, which is able to completely lock your magic — until you destroy the two crystal balls in his hands. His hard-hitting physicals make healing very important — for which you have nothing but items, which can't be shortcutted in this game. Game Over is imminent.
Anti Black Coat Nightmare in Dream Drop Distance has a particularly irritating one: he'll fire out a thin red line along the ground. If it hits you, it will lift you up in the air, suck all but 1 HP out of you, and scatter it around the arena as HP orbs! So, basically, you have to pick up all your health, while he's still attacking. Oh, and it's sometimes possible for him to use that attack just after he fires a barrage of weak shots. Immobile and on 1 HP, you have no chance of avoiding death in that situation.
Bonus BossJulius has a pretty big one too: he'll charge himself up with lightning, jump to the top of a tall building, then leap back down and bounce along the ground. It's really hard to avoid because of the AI's uncanny ability to know exactly where you're going to be when he jumps, so he usually ends up landing right on top of you. But that's not the worst thing about the attack. If he hits you, a random one of your commands will become greyed-out and have its reload rate slowed down so massively it's essentially taken out of the battle. Lord help you if he gets all your Curagas this way. Especially annoying is that, 9 times out of 10, the camera will lose your lock-on to Julius when he jumps, so you can easily get stomped simply because you lost track of where he was.
The Data versions of the Organization battles in Kingdom Hearts IIFinal Mix+ all follow a distinct formula, unlocking a very powerful attack (frequently called desperation attacks by the fandom) once you damage them enough. The game will force you to deal with this, and sometimes will not let you defeat the boss until you have triumphed over this attack (Demyx's 'defeat 99 water clones in 30 seconds' and Luxord's 'Do you know the rules?' minigame are good examples: do what you like to their HP, but you won't win until you clear those challenges). If you're lucky, the boss in question will only use this desperation attack once (like Demyx and his final water clone challenge). If you're unlucky, which you usually are, it will be added to the boss's pool of moves and reappear as often as the boss wishes. For example, Data Xemnas gets 'Can you spare a heart?', the move he used in the Final Boss battle as a one-time scripted event/gameplay element (the one where he drains Sora's health and the player is forced to use Riku), as a desperation attack, that he can use as often as he pleases after his health dips below a certain point. The good news? Since it is no longer a scripted event but a regular attack, it can now be blocked by Reflect, or Limits (as Sora is invulnerable while executing a limit). The bad news? You had damn well better block it, because Xemnas will drain Sora's health so fast this move might as well be a One-Hit Kill.
Romancing Sa Ga: Three words — Open the Gate. Death likes spamming this a lot; it pretty much kills your characters outright or heavily damages them.
Or even worse: Jewel Blaster, which deals magical damage, not physical. The Jewel Beast even spams it every three turns instead of six when you whittle his HP down. The "Overkill" you frequently see after Jewel Blaster isn't just for show.
Manah in the canon ending was a pain in the butt. She had this annoying attack in the middle of the fight where she would summon rings that came from her abdomen, not too bad. However, after taking so much health from her, she decides to summon the rings from all angles... Have fun dodging those.
In Paper Mario The Thousand Year Door, Magnus Von Grapple 2.0 has the Audience Cannon, which deals ridiculous amounts of damage if you don't have plenty of Defense buffs active. To a lesser extent, X-Yux has the attack that it uses when it has four mini-X-Yux around it, which deals massive damage and immobilizes; if it gets a chance to use that attack, the player is in serious trouble.
On the topic of the Audience Cannon, just like it says, it shoots the audience at you, for 3 damage per shot (which adds up to over 20 damage, which is almost always fatal in this game). And the audience is what you get your Star Power (essentially Limit Break) from.
One completely unguarded sequence of the Audience Cannon would probably not be enough to kill you in one go, although the reality wouldn't be much better, considering that at that point you'd probably have roughly 50 or so HP, so it probably would kill you in two.
The first Paper Mario game has Tubba Blubba's heart attack (Though it can be dodged by using Outta Sight), General Guy's Lightning Bulb Shock (xan be stopped by breaking the bulb), Huff n Puff's Lightning Shock (Which makes him immune to most attacks for a few rounds and does massive damage), and the Crystal King's Ice Beam attack (which does light damage, but inflicts the Freeze status effect on you). Finally, Bowser has several attacks, but the most frustrating one is his jump attack, which removes an option to attack from your menu (If you lose the Jump or Item one, you are screwed).
Even the Koopa Brother's super attack is painful at the point you fight them. Also, Jr Troopa when you face him in the Shiver Snowfield, when he uses his magic attack which does about 8 damage (which is powerful for this series).
The Shadow Queen's hands can use an HP-draining attack that deals 7 damage and heals 7 HP to the Shadow Queen, can be used once per hand, and ignores defense.
Two of Bowser X's attacks in Bowser's Inside Story. One is where he becomes giant, chases you down, and you have to dodge both fireballs being thrown at you and others you have to jump over while escaping him. If you get hit three times, you get knocked out and he pretty much crushes you flat. His Shy-Guy attack is also very nasty: it's kind of like a reverse Koopa shell, and if you miss, the brother takes a lot of damage. He also has an attack where he shoots fire, you hit it back, he turns into a fiery shell, drops a ton down from the sky that you have to hammer away, and then falls on you. If you do deflect his fall, he'll then fly off to land on the other brother. Did we mention how fast he goes?
In Bowser's Inside Story, the Junker seems like a fairly standard Flunky Boss...until he sucks Luigi up and sticks him inside one of his flunkies. The attack is unavoidable, unlike nearly every other attack in the game, and requires Mario to keep track of the Junker Can that Luigi is inside. In addition, the Junker Cans have tons of HP, they regularly swap Luigi around, and if Mario gets knocked out, you lose instantly.
Dark Star/Dark Star X and its cloning attack. Generates five to seven copies of itself, then charges at each brother. However, the copies turn INVISIBLE a short while before they reach your character, and long enough that you have to guess when to strike too. Miss that attack, and you get hit quite hard, often by another copy following the first one. On the plus side, a successful defense will likely knock out the next clone headed for that brother too.
The first attack used by Cackletta's soul in Superstar Saga. Because if you don't dodge, you will die instantly due to having only one health at the start of the battle (beforehand, you get blown up by a time bomb and eaten after a Hopeless Boss Fight). This is, of course, if your speed is lower than hers. Otherwise, you can heal immediately after the battle starts. The chances of you being faster than her are pretty low, though, since you'd've had to have leveled up to around level 34 and/or really focused on speed when using the level up bonuses and/or be using a badge that increase your speed and/or used speed up stat items.
There's also the giant laser/fire breath beam attack used by five bosses in Mario & Luigi: Bowser's Inside Story; Bowser, Dark Star, Dark Star Core, Dark Star X, and Bowser X. It does massive damage to the point of almost being a one hit kill, but is usually easily enough dodged. However, if one brother is knocked out, and the other guy is holding him, then it's quite difficult to catch Starlow and go to the top screen, likely killing whoever's remaining. Oh, and Dark Star does a kamikaze type charge at Mario/Luigi/Starlow if you dodge the beam, so if you forget to drop back down to the floor, it'll likely deal the same amount of damage the beam did.
The Elder Shroob Princess' last form in Partners in Time has an attack where her tentacle legs start spinning around her, forcing you to jump over them. It's not too difficult when she only has two legs, but when she has four legs, it's almost impossible to dodge. Couple that with the brothers flinching for a short time after getting hit so that once you get hit, it's impossible to stop getting hit, and you've got one incredibly annoying attack. Oh, did I mention it does a lot of damage?
In Super Mario RPG, the Breaker Beam attack used by Axem Rangers and later Gunyolk. Luckily, it requires charging for a turn or so, so you won't get nailed by it twice in a row. The charge-up also allows you to defend for the next turn so you'll only take half damage.
Any instant-death attack counts as this, unless you've equipped accessories that block them (or, for certain ones, have really good timing).
When Smithy is in his wizard form, Sword Rain, Spear Rain, Arrow Rain, and Dark Star count heavily. Also, his chest form uses different status effects on you, and Tank Form has an instant death attack.
Carni-Kiss is a really powerful attack. It's not a One-Hit Kill, but unless you explicitly do some grinding, it may as well be. And since it's technically a magic-based attack, you can't guard against it. A lot of the already-tough enemies like the Chest Monsters and Shogun pack it, which doesn't help matters. Very ironically, by the time you fight the Chomps that know it, it's not as dangerous.
Where are the aoe crowd control spells here? Petal blast? Light beam? Both of which will disable your entire party until the boss feels like pwning you? Seriously, any boss with either one of those attacks turns it into a luck based mission.
Culex and his elemental crystals have nothing but stupid-powerful attacks (like the aforementioned Water Blast), but none of them compete with his one physical attack. He doesn't even move to attack you, all that happens is you instantly hear a slash and one of your characters takes about 150 damage at a respectable level (for comparison, all of your characters are barely below 200 HP, and most of the magic attacks will only deal 50-70 at that point). And because of its unpredictability, it's pretty much impossible to block unless you instantly press A as soon as it's his turn to move. Even when you put the Lazy Shell on the Princess, which lets her take little to no damage from every attack in the fight, this attack will still deal about 50 to her. It's ridiculous.
Don't forget his Dark Star special, as well, which is armor-piercing and can pose a serious threat even to a Lazy-Shell-equipped Toadstool. At least it's only single-target.
Masa and Mune's combined form has an attack, signaled by the message "Storing Tornado Energy." and two turns later "Pain...", that does over 100 HP in damage and targets the entire party. At the time you face them, it will most likely knock your characters into the low double-digits and force you to waste a turn healing them. Even worse, the single obscure hint given by a random NPC that tells you how to stop the attack was mistranslated into uselessness in the original SNES release of the game. Attack Masa&Mune with Crono's Wind Slash attack (mistranslated as Slash in the SNES version) while he's charging the attack, and it'll dissipate the "Tornado Energy". Problem being that the man in the SNES version talks about you using Slash on Energy Whirls, whatever those are.
Energy Whirls are the enemy save points that appear in the pits in Magus's Castle; this isn't actually a case of mistranslation; the advice is entirely sound, it's just that the enemies in question don't have a name on the in-game combat screen. Although that NPC's advice DOES function equally well on Masa & Mune, that's merely a happy coincidence.
Magus risks casting a spell! (Signals that he's about to cast Dark Matter, his most powerful spell)
Barrier Change: Only Shadow damages! (Magus' Barrier Change spells not only make him immune to all magic except the corresponding element, they also hit the entire party hard. And he does them a lot)
Destruction rains from the heavens! (Lavos shoots his Spines of Death at you)
Lavos Core's "Grand Stone" attack, guaranteed to reduce you to single HP digits, if not kill you outright (but you can use this against him if you have Frog and/or Ayla in your party) Also Dreamreaver, which is basically the same attack, just a magic variant. Chances are it'll do more damage to your party than Grandstone. On the plus side, his attacks can be predicted. If you pay attention to the shifting background, you'll see his attack corresponds to the time period showing. This way you can at least prepare for the the pain that's to follow. Good luck with the actual damage though.
Any attack involving both of Giga Gaia's hands. The problem isn't the attacks per se, it's that, on a first run, Giga Gaia is almost guaranteed to go first and act twice in a row, and the Double Handblaster/Dark Plasma combo WILL Total Party Kill you if you aren't prepared (which boils down to having either insanely high resistance or outright immunity to at least one of the two elements he uses).
Son of Sun's flare and purple laser both take a huge chunk of HP (potentially over 300) out of pretty much any character who isn't appropriately equipped. While only Flare targets the entire party, its AI loop places the attacks right after each other.
The DS version adds a couple new ones, such as Scintillation. Thankfully only used by one boss, this attack deals an absurd amount of damage to the whole party - absurd meaning roughly 400 at maximum magic defense and with a Barrier that halves magic damage, in a game where the HP cap is 999. And if you have a character with less than maximum magic defense or remaining HP, better hope the boss doesn't recast it while you revive said character on top of healing your party.
Miguel and all of his white magic, but especially HolyDragSwd, which is so tremendously powerful it can almost one-shot anyone who isn't innately white. And he likes comboing it with WeakMinded, a magic-defense debuff. And if he manages to turn the field white...
Pretty much every element used by the Tragediennes. This is the entire point of them; if you can survive their initial volley of elements (and had the foresight to bring the right traps), you can acquire stuff like Volcano and BlackHole way ahead of schedule, essentially breaking the game wide open.
MegaStarky, otherwise a fairly easy boss, will smack the party with an UltraNova when his health drops far enough.
ExhaustGas, used by the Highwayman in the Dead Sea, blinds the entire party and is very accurate. You'd better have some BlackOut or Purify elements allocated, because you're not winning this fight with everyone blinded.
Dario's attacks are pretty much all crazy powerful, but special mention goes to one in particular. If you use any kind of white element in the battle, he'll counter with ConductaRod, a devastating black tech.
The Dragon God gets access to pretty much all the elements in the game, including nasty ones like BlackHole and UltraNova; when you add that to its already staggering magic attack, you've got a recipe for a party wipe. You can stop them with traps, if you know they're coming, but if you don't know about them, it's a long road back to Marbule.
Luther's Insanity Prelude in Star Ocean 3, an unblockable red flood that covers most of the battlefield. Assuming you aren't about thirty levels overleveled with equipment you shouldn't even have, its multiple shots will kill your entire party easily - you can only avoid it by standing in certain corners of the battle map - and forget your AI-controlled party members going there, you have to guide them all manually. (Alternatively, you can stun him out of casting it.) Any SO3 message board is inevitably hit with 'how do I dodge Insanity Prelude' more than a few times.
While several of the Nintendo Hard extra bosses have similar moves, the final three of Lenneth, the Etherial Queen, and Freya are by far the worst. With Lenneth and the Queen, you at least have a slight chance of making it to the edge of the screen to dodge Nibelung Valesti and Celestial Star. Freya, however, will spam Ether Strike again and again without warning and cannot ever be disrupted. You only hope is certain stunning items which buy you a total of, oh let's say, three seconds, before she's back on the offense.
The trick with Ether Strike is to make sure she's nowhere near the center of the battlefield when she uses it. The move is slow enough that you can make it to the other side of the field, so it's in your best interest to simply keep her pinned on one side of the battlefield by luring her there. The first minute or two of the battle can be pretty rough though, as you must survive her attacks long enough for her to GET to the battlefield's side. Or alternatively, abuse Fayt's Side Kick which has invincibility frames and lets him completely dodge it...
Fadroh in Baten Kaitos is a Curb-Stomp Battle. Who is curb-stomping who? That depends entirely on whether or not Fadroh buffs himself with Orb of Magical Offense.
Geldoblame's Forfeit Your Life, a One-Hit KO. And he likes to use another attack called Seal of Evil, which paralyzes a character, meaning they can't defend.
The Angel of Darkness also likes paralysis, but couples it with an attack that steals your HP. When he Turns Red and moves twice per turn, it's not uncommon for him to heal faster than you can damage him.
Agyo's A-Up Pentagram. Not a One-Hit Kill, but might as well be.
The Holoholobird's Wingflail, which knocks the whole party down and breaks any combos you've set up.
The Godcraft's hail attack. It hits the entire party for tremendous damage, enough to cut over half their health down.
In what might be either a bug, a programming oversight, or just the dev team being sadistic, that attack (and several others used mostly by bosses) are lethal if you have a party member knocked out. Essentially, they're programmed to hit the whole party multiple times, but the targeting is random, i.e. the attack might not even scratch Guillo, but knock Milly out and put Sagi in the red. However, if one of the party members is down, the attack only has two targets, but it still hits the same number of times, meaning the two remaining are in for a world of hurt.
Wiseman's Cast Off Your Carnal Robes. Doesn't do too much damage, but it knocks the whole party down, destroys any magnus you have equipped, and breaks your combos. Just to add to that, he steals your magnus power with his regular attacks, so you'll be seeing his specials a lot.
Magnus of Life, used by Verus-Wiseman. It hits the entire party, hurts like hell, heals the boss, and inflicts all status ailments. Nothing's better than losing just because everyone's blinded or frozen.
When you see the eponymous boss of Diablo II step back, run like hell because he's about to unleash a brutal stream of red lightning◊ that can sap your health in seconds. This was nerfed in Lord of Destruction, but it's still very damaging: it can still take most of your health in a single second, if not actually kill you. Diablo's ring of fire, his other attack, hits everything in every direction even when he's not on the screen, making it essentially unavoidable.
There are various bugged monsters that can nearly instantly kill you. The hardest two are poison vipers, whose poison javelin is bugged and deals their regular attack damage 25 times per second on top of its poison damage; and gloams, who seem to deal 256 times their intended damage.
Some enemies in Dragon Age: Origins will use the same Game Breaker abilities that you use all the time. It's no fun at all being on the receiving end of a Crushing Prison (continuous damage and paralysis), Overwhelm (essentially a physical version of Crushing Prison), Scattershot (ranged mass stun that's almost impossible to resist), or "Curse of Mortality" (negates healing and does continuous damage). That last one is almost guaranteed to result in character death (which is extremely annoying if you're going for the "No Deaths" achievement) unless it's dispelled. Some bosses such as the High Dragons also have grab attacks that can instantly kill any of your party members except for the unique ones like Dog and Shale, which makes those two good choices for fighting against Flemeth and the High Dragon. You will also quickly hate the Revenant's "Pull" attack when it brings your precious mage or archer within range of that BFS.
There is only one thing worse than Pull: Mass Pull. Nothing beats getting all your party members yanked off their feet and into melee range, often interrupting vital spells or talents.
BLOOD WOUND. It's like Crushing Prison, only for your whole party at once! Very likely to end your game. Always shoot the blood mage first.
The Limit Break of the final boss in Tales Of Graces kills at least two of your party members, unless you're fighting on easy mode. If you're unlucky, it will obliterate your entire party.
Also from Tales Of Graces, there's Emeraude with her Killing Field spell she always uses immediately after entering Arles Rise, which hits the entire battlefield, and is likely to put everyone into critical HP or KO them on higher difficulties if they don't defend against it (Which the AI is quite prone to).
Tales Of Symphonia has Retribution, which the first form of theFinal Boss uses — and then adds to its A.I. Roulette — when you get him down to about half of his HP. It gives two random status ailments to each of your party members. The catch? It's unavoidable, unstoppable, and chances are that two of said party members are going to be poisoned (and at least one of them paralyzed).
There is a way to stop the attack, actually. The tech name shows up on top of the screen about 2-3 seconds before the effect actually takes place. As soon as you see the tech name on top of the screen, run up to the boss and start a Unison Attack. If you do it in time, Retribution is canceled out, and the boss won't use it again unless the HP requirements are met, or he decides to use it at random.
Big Bang is even worse in the PS3 version, as it actually has the capability of killing you on higher difficulties. Did I mention that it can do upwards of 80,000 damage on Unknown mode (meaning even Flynn's Energy Coat can't save you)?
The optional bosses get pretty bad too. Philia has Big Bang and Sacred Penance which both are usually guaranteed to hit you. Reid also can use Aurora Wall. Hits everyone nearby, which isn't bad... but did I mention that it REVIVES the fallen comrades? And Nebilim... Big Bang, Mystic Cage, Fortune's Arc, Indignation, Rending Saber, Radiant Howl, and the worst one yet, the only one she didn't steal from your party members... Fragmented End. Basically? If she does this... you're gonna be reeling if you survived.
In Pokemon Diamond And Pearl, Lucian's Bronzong has an incredibly frustrating one: CALM MIND. Bronzong is one of the most difficult Pokémon in the game to KO with physical attacks, so naturally you're encouraged to go with special attacks. What does Calm Mind do? It increases Bronzong's Special Defense AND Special Attack, so not only is it nigh impossible to knock out after a single use, its attacks are much stronger. Worse, Bronzong can use this up to six times. After about 4, ALL of Bronzong's other attacks are That One Attack, and it only gets worse from there. Thanks to this, Bronzong, by itself, is more difficult to defeat than the Champion'sentire team. Which is why Bronzong was nerfed a full 11 levels in Platinum. And There Was Much Rejoicing.
In Gen. I, if your Pokémon is slow enough, "Ekans used Wrap! Ekans's attack continues!" Again and again and again. (This was fixed in the later games. Wrap no longer holds your Pokemon to keep it from attacking.)
On the other hand, this nerf made Wrap relatively useless, since the damage on its own isn't anything to write home about. It does prevent the target from switching out, though.
Wrap can still annoy the heck out of you in the Pokémon Mystery Dungeon games if you're slow. Lileep loves this move in particular.
The foe's Clefable used Metronome! The foe's Clefable used Volt Tackle! It's super effective! Gyarados fainted!
This has been changed in later games to be dependent on level - the higher the level the attacker compared to the target, the more accurate it becomes. 30% is now the minimum, with an additional 1% per level difference.
On the topic of attacks hitting more often than they should, Hydro Pump, Blizzard, and Thunder are notorious for not always hitting. However, the computer will always hit if you're at all weak to the attack.
The foe's Alakazam/Mewtwo used Psychic! (In Gen. I, though it can easilly OHKO anything without explicit resistence.)
Stealth Rock. It creates an "entry hazard", which means that any further Pokemon who switch in will take damage. At least Spikes and Toxic Spikes could be dodged with a Flying-type or somebody with Levitate... but not Stealth Rock. Unlike dealing a set amount of damage on Spikes, it factors type matchups into the damage done. Which means that somebody who is weak to Rock losing a quarter of its health, and somebody with a double weakness losing half just from being sent in. And that's not all- during the Generation IV metagame, it was everywhere. It had the effect of making Fire, Flying, Bug, and Ice-types effectively useless (especiallyCharizard), and may have led to more of a focus on the usage of Ground, Steel, and Fighting-types, as well as Pokemon with the Magic Guard ability. It was so bad that Generation V heavily nerfed it: it restricted the amount of Pokemon that could learn the move (it was learnable by TM back then, but said TM was removed in Gen. V; starting in Black 2/White 2 it could be tutored to a select number of mons, though). Mirror Coat was buffed to reflect entry hazards, as well. It also added in an Ability that reflects incoming status moves/entry hazards (Magic Bounce); the possessors of said abilities note Xatu and Espeon rose in rank in the metagame merely because of this.
Any Psychic-type move, but especially Psybeam, Dream Eater, and Psychic. Unless you're using a Dark-type, watch out. Wait, you're playing Red, Blue, or Yellow? Sucks to be you! Also, Hyper Beam for any Dragon-type.
Earthquake. Sure, it's a move with good power and great typing and accuracy. However, said type is one of the strongest in the game. But that's not what makes it so bad; what makes it bad is the fact that it is absolutely everywhere. The chances of a high-skilled team not having the move are slim to none, and an immense amount of 'mons can learn the move. It also hits everyone that isn't immune to it.
Wild Voltorb used Selfdestruct! Or worse: Shiny Graveler used Explosion! Koffing/Weezing are notorious too...though a Ghost as your lead or Rain Dance nullifies it.
Whitney's Miltank used Rollout! And if you're playing Heart Gold? Miltank used Stomp. *insert Pokémon you're using here* flinched. Even if it's a Ghost-type, due to Scrappy ability.
On that note, any move that can cause Pokémon to flinch. For every tale of glorious victory by causing the enemy to flinch, there are several others mourning the loss due to having a 'Mon flinch at the wrong time. One of the most annoying could arguably be Fake Out which 1) Is a priority move and 2) Always flinches, wasting a turn.
Any attack that causes confusion, particularly Confuse Ray. Since The Computer Is a Cheating Bastard, the next 5 turns will have your Pokémon "hurting itself in its confusion". Naturally, that's only true for YOU as the computer will snap out of it in 2 turns and won't hurt itself once. Confuse Ray make it worse: it's 100% accurate, and pretty much every trainer with a Zubat, Golbat, or Crobat has this attack on it, and will be more than happy to use it on their first turn.
The foe's Shiftry used Swagger! Swagger, while not 100% accurate, also causes confusion. It also doubles the target's attack. So, in the event that you hurt yourself, you'll do twice as much damage to yourself as normal. And the damage boost stacks. Oh, and anyone that can use TMs can use it! Fortunately, if your mon has the confusion-preventing Own Tempo ability, it simply gives them a free Attack doubling. If not? Good luck.
Cotton Guard, for anybody who relies on physical attacks. It raises Defense by three stages, which essentially means that a mere two turns of use maximizes Defense. Which means a 400% Defense boost. This basically means that, unless you get lucky enough to get a Critical Hit, even super-effective attacks will do Scratch Damage. Oh, and guess who can learn it? That's right, Whimsicott!
In Gen. I, anything with Poison Sting. The AI has an irritatingly high chance of poisoning you if you don't KO the opposing 'mon within a couple turns, sending you straight back to the nearest Pokemon Center.
Double Team. There's a reason why it's almost universally hated, and if there are any moves that people agree to ban from a battle, that one's right at the top of the list. Worst of all, the AI gives that move out to their Pokemon like Halloween candy and it has a tendency to make even your 100% accurate moves miss after just one use.
Protect, while not nearly as bad as the others, is still really annoying and makes you waste a turn and PP. If the AI at least used it strategically it'd be one thing (since you could still counter it with the attack Feint), but since it's purely A.I. Roulette they end up using it just because, even when it's obvious that you've already won and it won't help them thus they just delay the inevitable. The problem is that no one in their right mind would run a moveset with Feint on it, especially with the nerf. It now deals 30 damage (at least before, the damage of 50 could be bumped up to 75 with Technician), but now, even if you factor in a STAB and Technician, you aren't going to be busting 70 power with it. Meanwhile, its only use is to defeat Protect and Detect, both of which are not worth the trouble. Shadow Force, the only other attack that can counter Protect, is only available on Giratina, so if you don't use legendaries, good luck.
Watchog used Retaliate! note Retaliate doubles in base power (from 70 to 140) if a Pokemon on the user's team fainted in the previous turn, and when you factor in STAB, that jumps up to 210. No, really. This move can be found on the second leader's Pokemon, and if you're not ready for it, Lenora will plow you like fresh snow.
The foe's Clefairy used Encore! (and now you're stuck on one move until you run out and only have Struggle left. You might be able to wait it out if you can switch out, have enough HP on your moves or if you've got some PP ups, but if you happen to be on your last Pokemon...)
In multi-player games where items are allowed to be used, a Nidoking can easily turn into one of these back in Gen. I. One-hit KO moves have an accuracy of roughly 45%. X Accuracy doubles that. NIDOKING used FISSURE! It's a one-hit KO! Repeat four more times, and you will still have six pokemon to one when you lose all PP.
If there's one move that trainers dread seeing Zebstrika use, it's "Flame Charge". This is because not only is Flame Charge super-effective against Grass-Type Pokemon (which normally have a resistance against Electric-Type attacks), but it also boosts Zebstrika's already very high Speed stats. Oh, and it loves to spam this move several times. This means that now it is insanely fast and can easily strike with moves like Spark, Thunderbolt, and Charge Beam several times (and paralyze your Pokemon with said attacks) before you get a chance to do much damage.
Audino/Minccino/Clefairy used Attract! Your Pokemon is in love! Your Pokemon is immobilized by love! What's worse is that unlike moves that cause confusion, Attract doesn't wear off after a few turns. You have to switch out in order to cancel out its effects while in battle. Luckily, it is negated by the fact that Attract doesn't work on genderless Pokemon or Pokemon of the same gender as its opponent.
Roost. A Flying-Type move introduced in Gen IV. It became especially annoying in Black 2/White 2 where Tranquill just adores spamming it to no end. What would normally be a quick and easy battle turns frustratingly long since Tranquill will constantly use it whenever its HP starts running low.
It becomes an even more annoying move to deal with whenever Tranquill decides to use both it and Detect. Good luck dealing with a Pokemon that loves to both render your attacks useless and constantly replenishes its HP as well.
In Pokémon XD: Gale of Darkness, if you aren't using Shadow Pokemon against Gorigan...."Snorlax used Shadow End!" It's the shadow equivalent of Double Edge, and since Shadow is super effective against everything else, anything that's non-shadow will take a lot of damage.
Body Slam. It packs a punch and has a whopping 30% chance to cause paralysis. Paralysis is annoying because it reduces you to a crawl on top of having a 33% chance of not being able to attack. On top of that, a ton of mons could learn it in the first generation, and there it was the equivalent of Stealth Rock- hard to deal with and very widespread.
Memento, especially so in the Mystery Dungeon series. It gives a nasty offensive debuff but at the cost of the user fainting... except it's worse in Pokemon Mystery Dungeon, where everyone in the room gets this debuff, and the user simply teleports away (with only 1 HP), instead of fainting, free to use it again.
The evil storyline of Champions Return To Arms has Mithaniel Marr as the Final Boss. And one of his attack sequences involves throwing you to the ground while dealing immense damage, and then attacking several more times while you can't move.
This only applies in single player mode, however, with two or more this attack is a great way to get a shot at his back.
In Runescape, the final boss of the quest Nomad's Requiem, the eponymous Nomad has an attack in which he freezes you in place, then charges an attack that does damage equal to your maximum health minus one hitpoint. There's no way to avoid it, and unless you have maximum health when it hits, you die, instantly. That was the case until "damage soaking", which made this attack less scaryMechanics When you would be hit for 200+ damage, the part of the damage which is 200+ is reduced by several-severalteen percent, based on your armour. This usually is useless, but against Nomad, which can hit for 750 and for MAXHP-to-One, this actually makes some visible impact.
Most of the Dungeoneering bosses are just normal bosses with One Attack that makes them special. The Luminescent Icefiend is notable - at every 25% HP milestone, it becomes invulnerable, then sends down a painful icicle rain attacknote that takes just about two seconds to fall down and is fired at a rate of one per 0.6 seconds, which is as often as possible. The attack doesn't deal much damage per hit, but if you get hit by one, you are thrown aside and generally assured to be hit by a dozen more. Luckily, it stops before you die. The only way to avoid it is to keep moving - if you stop for even a second, bang. The fact it targets an area and not a player is especially frustrating - if you're in a large team, then crossing paths with someone can mean being hit by an attack meant to hit him. Night-Gazer Khighorahk has a melee attack that hits everyone around him for heavy damage, too - if you don't run away when you see it charging, you take heavy damage. Saggitare's arrow rain works the same way.
Even player-killers have their own That One Attacks, such as Ice Barrage, which freezes the target in place, but can be cast over and over, lengthening the effect. It basically leaves melee fighters helpless.
In Mother 3, Porky has an attack that he, thankfully, rarely uses where he "coughs something up." It is the equivalent of using Offense Down AND Defense Down against your entire party 3 TIMES, and can be dangerous if you don't have enough PP to raise your stats back up.
From EarthBound, you have the Kraken's tornadoes. They do huge amounts of damage, hit everyone in the party, and can't be nullified or deflected like his other attacks can. Also, buffs won't help you; the Kraken's only nonoffensive attack neutralizes any buffs or debuffs you might have cast.
Also, Diamond Dog's 'glorious light' attack. Anyone without certain equipment will most likely get paralyzed, killed, or confused. You're in trouble if you missed the Sea Pendant at the far end of the Lost Underworld.
Made even worse when Ness's Nightmare uses it. If Ness has a Night, Sea, or Star Pendant, it'll just waste a turn. If you gave that to a weaker party member, then you'll be up against an attack with a good chance of either being a one-shot kill, paralysis, or confusion. Against a Duel Boss, that's a very bad thing.
The preferred attack of a few Metal Slimes from both games (Criminal Caterpillar and Master Criminal Worm from EarthBound, and the Beanling and Black Beanling from Mother 3) is a low-level PK Fire, which hits your entire party For Massive Damage the first time you can possibly fight them.
There are a lot of attacks in Mother 1 that you will hate. Dehydration attacks, which lower your offense and defense at once, are nasty, as are last shot and PK Beam Gamma attacks which can instantly kill someone. Was it mentioned that you have to go back to town to revive a party member? And that the instant-kill attacks can be used by enemiesbeforeyou get your second party member?
You can't mention the Tail clan without talking about Annihilator Hadoken, which deals an insanely high amount of damage (sometimes reaching into the tens of thousands). Also, if it doesn't deal enough damage to instantly kill a party member, it has a high chance of inflicting Crash (at least while fighting Ninetails), which means that they'll still die.
Epsilon has Meta Crash. It's an HP To One attack that never misses (unless it targets Stealth Mode Axl). Epsilon will open the fight with this move, and he spams it after he Turns Red. He likes to follow that up with Nova Thunder, which deals immense Electric damage to everybody.
Silver Horn's Liquid Coating doesn't do any damage, but it is a very irritating move. After using it, his defenses skyrocket, and he has a chance to arbitrarily guard any attack, so even Thunder - his weakness, what he's supposed to take more damage from - does minimal damage to him when he blocks. It also allows him to use Pressure Abyss, an Ice attack that is always a Critical Hit.
Atomic Fall, used by the Meltdown. If you can't kill it before it takes three turns, you're looking at a suicide attack that does high 4-digit damage to your entire party.
Bass from Mega Man Battle Network 4 and onwards gets his Buster Rake upgraded. Instead of shooting rolling shiny balls down the rows, this one actually rakes your side of the field several times, does not provoke Mercy Invincibility, is insanely hard to dodge, and the faster he gets, the harder it is to dodge, all the way up to being completely undodgeable. Sure, a single Panel Grab chip will eliminate this, but few people actually bother with it. And in his final forms, every hit deals over a hundred damage, which piles up fast. No matter how high your HP counter is, it's all reserved to tank Buster Rake. He also LOVES to finish off low HP with this.
In Battle Network 5, Shademan's attack in Liberations has practically infinite range; it can hit anyone next to a Dark Panel. It doesn't matter if he's still within locked panels or if you're on the opposite side of the map, he can still hit you.
Speaking of Liberations attacks, Dark Cloud. The damage it does isn't so bad, but it paralyzes anyone in the attack's range, meaning that you have to wait a phase until they can move again. God help you if you tried to rush Cloudman with all your Navis.
Rewinding to Battle Network 3, there's Kingman's Plan B. He uses an Area Grab to reduce your running room, moves his Pawns as close to you as possible, and summons a Knight in your side of the field. Let him live long enough, and he'll do it again, this time using only one Pawn and two Knights, again in your field.
Players of Yggdra Union often cringe when the word 'Genocide' is mentioned. It's the signature move of That One Boss Gulcasa which kills off his allies, giving him an exponential boost in power for every unit killed. To make matters worse, this move shatters your meter, preventing you from using any cards to defend yourself with. Finally, if he manages to take out all your characters with this move during a skirmish, your morale takes quite a plunge. Oh, and did I mention that you have to face this guy quite a few times?
Players of Blaze Union may cringe when the word 'Jihad'note English-speakers that played Yggdra Union may call it Crusade instead is mentioned. It's the signature move of Ordene, which immediately causes him to win if he is alone and at MAX Rage Rate. Oh, and you can't block it with Shield Barrier. Good luck with that. There's a way around it; he won't attack Aegina with it.
On that note, Bonus Boss #367's Judgment Zero. In her first form it's barely worth mentioning, but in her second form it is practically guaranteed to do Overkill damage, which is an instant loss for you. Like Jihad, it is unblockable and non-elemental, so if she gets it off you will die. It's a lot more manageable in Blaze and Gloria, where it will only deal Overkill damage if Alanjame or Gariored is alone.
And speaking of Gloria Union, Megiddo. It's basically Crusade with a smaller Morale damage bonus, but its user doesn't have to be alone. Once again, it's non-elemental, and Shield Barrier and the new anti-Skill skill Magic Shield do nothing against it.
Many players in City of Heroes have learned to fear Ghost Widow. Her darkness based powers are tough, but manageable. Where she really hits you hard is her signature attack Soul Storm, which is a magnitude 100 hold that deals continuous damage for several seconds. The average magnitude of a hold (including the player version of Soul Storm) is 3. Any character hit with this has a very high chance of dying.
A close follow up (also from Ghost Widow, though it's available to custom AVs as well) is Dark Regeneration. Dark Regeneration is a mild AoE attack that grants hitpoints depending on how many foes are successfully hit. On a heavily Melee oriented party, this is bad. On a party with one or more Masterminds, this is very bad. Thug and Demon Summoning Masterminds should be particularly wary, as their signature powers (Gang War and Hell on Earth, respectively) amount to what is basically a full heal if used against a Dark Armor wielding Archvillain.
The Dilemma Diabolique trial had several attacks. The Sentinel of Mot had a (thankfully optional) power that created a difficult to see white circle around him. For every person within this circle, it would rapidly regenerate hit points.
The Underground trial had several instances of annoying. The War Walkers had targeted abilities that grew in power depending on how many people surrounded the marked player. Don't notice and forget to run? Total wipe. Did I mention this part is an Escort Mission? Thankfully, most groups left the NPC upstairs. What was even more annoying was the timed battle against the Avatar of Hamidon, which featured an automatic Confuse effect that required multiple applications of Status resist powers to avoid. If someone didn't notice the "confused" tag on their status bar, they could end up murdering the entire raid, or worse: HEALING THE BOSS.
Thresher maws in Mass Effect continually burrow into the ground and reappear somewhere else. That "somewhere else" can be directly under you. Instant game over. That isn't even getting into its actual attack, spitting out acid which completely ignores your shields and take off more than half of the Mako's hit points (if you're fighting on foot, the acid attack is very likely to insta-kill). The general strategy people recommend for thresher maws is "run the hell away."
Biotic enemies love to spam an ability that knocks Shepard down, leaving him completely helpless. Fighting against multiple biotics means that you can be stuck to the floor for quite a while, watching your health whittle away without being able to do anything about it (even pause the game).
The rocket drones in the Luna base frequently fire extremely powerful rockets. They're almost guaranteed to be a One-Hit Kill unless you have high-level Immunity or very high shields.
In Mass Effect 2 there are a lot more examples of this trope. There are the Scions, whose Shockwaves tear your shields to pieces and ignore cover. There are the Praetorians, whose Death Choir attack decimates anyone within blast range and fully recharges their Barrier. There's the Oculi, whose energy beams stagger you and deal massive damage. There's Harbinger himself, who's fond of using a Singularity attack that knocks you out of cover so he can bombard you with Warp blasts.
In Mass Effect 3, Banshees have a homing Warp attack that inflicts lingering damage, a Nova-like attack that strips shields but is unlikely to kill, and a claw swipe. These are all annoying, but manageable. They also have a One-Hit Killmelee attack, coupled with a generous definition of "melee." Other enemies, like Phantoms, Brutes, and Atlas mechs, have instant-kill attacks, but they can only use theirs as a follow-up to a regular melee attack, while the Banshee can grab you the moment you enter its Instant Death Radius.
It's not unheard of in World of Warcraft, either. Deathbringer Saurfang, for example, has an ability called "Mark of the Fallen Champion". Players marked by this ability will take massive damage for the rest of the fight, and if they are killed, he will heal himself for a significant amount. You basically just have to pray he doesn't target a Squishy Wizard, or you're screwed.
The bosses of Mount Hyjal seem to have this fairly often. Rage Winterchill, the firt boss, has a Death and Decay that does 15% of each victim's maximum health per tick. Azgalor has an attack that targets a player every 45 seconds and kills them after a 20 second debuff expires. Archimonde can fling players into the air with Air Burst, and they must know how to use the Tears of the Goddess correctly, or they will fall to their deaths.
Because of multiple That One Attacks coupled with his status as That One Boss, Archimonde was considered unfarmable by some servers, even after he was nerfed for Wrath of the Lich King.
Toward the end of Wrath, if you mentioned the word "Defile" in trade chat, everyone knew what you were talking about. To those not in the know, Defile is an area of effect attack used by the Lich King. He frequently casts it beneath a random player, and its damage and size increase every time someone stands in it even for one tick. If your 25 player raid group mismanages this ability? You're dead. To make matters worse, he has another attack that is handled by stacking close together, and since both attacks are on a slightly different timer, they occasionally come out back-to-back. Defile is the reason that, even at the end of the next expansion, when a single character has ten times more health and can output more damage than an entire raid party used to be able to, it still takes a coordinated effort to defeat the Lich King.
Even going as far back as classic, C'thun had his infamous Eye Beam attack, which would blast a player for respectable damage before bouncing to another, its damage doubling each time. Many stories were recorded about entire 40 man raid groups entering the room at once and getting slammed by this, the very last victims suffering hits in the hundreds of millions. This attack may qualify in-universe for Memetic Badass status, to the point where people have sat down and thought up strategies to maximize its damage, such as taking 40 hunters with 40 pets and having them drop 40 Snake Traps.
The final boss has "Subjugation", which will cause your character to surrender the battle, no matter how many hit points either of you have left.
Bonus Boss The Yeti has "Crushing Blow", which does 999 damage (which is about five times the HP you'll probably have when you first confront him).
.hack has several. The first game has Skeith's "Judgment", which hits the whole party, is impossible to avoid or block, and hits for roughly 70% of your health. Then there's Macha's attack which inflicts Charm on the whole party... which means they beat each other up until it wears off, and you can't heal it because it hits the entire party. All of the Phase bosses are also capable of Data Drain, which only targets one party member but destroys their HP and infects a number of status infections. And it can be spammed.
In Dot Hack GU, there's Azure Kite's "Azure Tiger Claws". It is possible to block this, but it requires some very tricky timing: the attack is timed so that if you do a full combo (which is what most players instinctively do), it will hit you during the lag between attacks. Later, in Redemption, there's "Chaos Gehenna", used by Cubia Alpha. Once his HP hits around 20-30%, he simply spews a long stream of Gomoras at you. It's next to impossible to dodge, and harder to destroy all of them without taking damage. Also, since this is an Avatar Battle you cannot heal, and if you lose you must restart the battle from the Cubia Beta phase.
There are more than one here, but the Megiddo technique from Phantasy Star IV deserves notice. It was a staple attack-all ever since the second game, and suddenly, the final boss has it like your main character. (In addition to sucking up souls or whatever before performing.) Absolutely devastating when the boss decides to remove your buffs, and man can it spam like there's no tomorrow.
Breath of Fire: Dragon Quarter has Malefactor, used by Dragonized Bosch. What it does is afflict the party with every status in the game. So unless you're going to unleash everything with Ryu's powers, you're gonna want to have even one person with immunity to bail the others out (if not more).
Late in Seiken Densetsu 3, many level 3 techs when used by the enemies, such as Split-Image Slice or Vacuum Sword, will hurt everyone in the party for around 80-90% of their max HP. These attacks can take a fully healed party to critical, or a party in decent shape to dead. If two of these are used on you in a row, you're just screwed. And keep in mind, these are attacks done by normal enemies.
Enchanted Arms has bonus boss Omega and his Near Death Edge, which, true to its name, instantly chops the HP of anyone hit by it down to 1... and to rub salt in the wound, it also cancels any and all buffs and barriers on the victim, which makes the usual anti-boss tactic of setting up a 90% damage reduction via Raiga's Tiara Crusade more or less worthless. On the flip side, beating Omega allows you to recruit him... and he still has Near Death Edge, which works on absolutely anything in the game. Yes, including the final boss.
The spell Abi-Dalzim's Horrid Wilting in Baldur's Gate 2. On paper, it does 1-8 damage per level of the caster, half on a successful save...but a mage has to be level 15 to know it, meaning an awful lot of damage is being thrown around. This is somewhat unfair when you are a Squishy Wizard with less than 40 health and oh sorry just failed your saving throw, time to reload. Especially since unless you were a very dedicated grinder you are still two levels away from being able to cast it yourself (which is, admittedly, very therapeutic).
Everything used by Sirius in Mega Man Star Force 3. Satellite Blazer, his signature attack, hits every tile of the field and can't be blocked (or dodged for that matter, unless you have Air Shoes). Another favorite move of his is Wing Formation, in which he detaches his wings, which start shooting elemental lasers. He has four wings, so one column of the field will invariably have a double-element attack going on. Again, unblockable and also unavoidable; the only real way to survive this move is to keep getting in columns that don't knock you out of a Noise.
Apollo Flame in the second and third game has an attack where he drops a miniature sun on Megaman's side of the field. This attack comes out very quickly, it can't be dodged or blocked (unless you knock him out of it first), and it cracks the panels on your side of the field.
The final boss of Skies of Arcadia brings us the Silver Nightmare attack, where he possesses one of your party members and forces them to use one of their special moves against one of their own allies. It has priority over EVERYTHING, even defensive moves like Justice Shield, and is the only damaging move in the game that has this high a priority. And the possessed party member loses their action for that turn, and quite often you will see him turning Vyse's Pirates' Wrath into a One-Hit Kill of your Squishy Wizard, making that two actions in one turn you just lost, and often more because you get to watch your characters uselessly start using their shield moves. Have fun catching back up with the battle flow!
As far as ship battles are concerned, there's Bluheim's Blue Winds attack. While technically by itself it does the least damage out of Bluheim's attacks, it causes the entire next round to be filled with nothing but tiles giving an advantage to Bluheim, which is just as painful as it sounds. The only other attack in the game that does this (Auriga's Hull Ram) is easily avoidable by casting Quika; no such luck for Blue Winds.
Flash game Sonny has Baron Brixius' Tick Tock debuff, which deals damage equal to 10% of the victim's maximum HP... and continues to do this for 10 turns. It also cuts any healing they receive in half, can be cast on multiple characters at once, and can't be removed by status-removing spells. Note that this game has no multi-target healing and no way to revive dead allies. Note also that Baron Brixius would be a Marathon Bosswithout this attack. With it, he becomes That One Boss. The only saving grace is he likes to use it on himself if you last long enough.
Almost every class has an ability that reverses damage and healing, seemingly for little reason other then to make this one fight easier. In fact, in one portion of the fight, he will begin spamming an ability that heals a third of his health, this is when you stop inverting damage on yourself, and instead concentrating all the love on him.
Suicide is exactly that - a monster that is threatened will explode, taking you with it. Of course, there are some cases where a monster will Suicide while not actually having taken damage already...
Banish is the bane of Freebie Newbies - If you're inside the banish ring after three seconds, you get instantly teleported to The Hub. Most bosses have this as an anti-Tank measure, and one set of boss trials have an entire room dedicated to not getting hit by Banish (while still getting hit by skills that keep you from moving at all)
Berserker significantly increases the user's attack power (AP). When a player uses Berserker, they also lose control of their character until the effect ends, and the game selects nearby enemies at random (read: if you use Berserker while in the middle of a crowd, you will do nothing for the first five seconds), it blocks you from using skills, it reduces your health as long as it is active, it lasts for 20 seconds, and you can only start it once every 30 seconds. When a monster uses Berserker, it lasts for 30 seconds, the cooldown is 20 seconds, they can use skills, and they start moving faster. Heaven help you if you come across a monster with both Berserker and Guard Break.
In Xenoblade Chronicles, Jade Face/Gadolt's Laser Cannon does an absolutely massive amount of ether damage that can easily OHKO party members with lower max HP values, has a huge hit radius that makes it almost guaranteed to hit everybody, and leaves them dazed if they do survive. If you lack the few means of mitigating ether damage effectively and/or aren't of a significantly higher level then him, it can make winning extremely difficult.
In Epic Battle Fantasy III, there's Doomsday, used by Cosmic Monolith. It deals huge dark-elemental damage to everything on the field - but Cosmic Monolith actually absorbs dark, meaning it can bring your whole party to near death while healing itself. The attack is used every three turns, so if you can't outdamage the healing (taking into account that you also have to recover your health in meantime), you're screwed. An optional fight with two Cosmic Monoliths is actually harder than the Final Boss.
Dark Souls has quite a few. Chaos Witch Quelaag has a devastating area of effect explosion attack; even with high fire resistance, it's likely to stagger you and take off quite a chunk of health. It's telegraphed well in advancenote When Quelaag hugs the spider, run, but if you don't get your shield up or get away, you'll get your face blasted off.
Grappling attacks are unblockable and will usually take off at least three quarters of your health bar every time you're grabbed. Sure, they're telegraphed, but if you're focusing on finishing off another monster or overestimate your dodging ability, it's very easy to get an amateur tracheotomy courtesy of an Infested Ghoul's teeth, or pecked to death by a Crow Demon, or chewed on by the Gaping Dragon, or stabbed through the chest by a Wailing Ghost, or smashed into the ground by the Iron Golem...
The Basilisk's attack, which spews a gray cloud of fog that causes curse. Curse is easily the deadliest status ailment in the game, and extremely hard to remove.
"Off Waves", Tabuu's instant-kill red ring attack from Super Smash Bros. Brawl. It hits thrice in a row, but once is more than enough if your dodge timing is the tiniest bit off. And that's after it was weakened by Sonic smashing the wings he extends to perform it. In a cutscene beforehand, he was able to OHKO most of the cast at once. To make matters worse, in Boss mode on Intense if you slip up once on this attack it could send you back to fight all of the other 9 bosses again.
Master Hand and Crazy Hand have their hand drill attack which is difficult to avoid and capable of dealing up to 90% damage in Brawl. As well, Master Hand's finger walk has been improved in Brawl to have almost no starting lag and move quickly. Woe betide the player that happens to be right next to Master Hand when the attack executes.
Quite a few characters have what could be described as Skill Gate Attacks as well. Meta Knight's Tornado and Shuttle Loop, Snake's up tilt, Diddy Kong's bananas, Falco's lasers... all are counterable if you know what you're doing, but they're still quite powerful.
Pit's Angel Ring reflects projectiles, tends to draw enemies inward rather than push them back, and has a massive range which sucks in even opponents melee attacking from behind. Worse, it can continue indefinitely. Very few attacks can put a stop to a player spamming Angel Ring.
Meta Ridley has an attack where he drops onto the Falcon Flyer, the only solid ground you have while fighting him. It's a One-Hit KO if you don't have the timing required to dodge it.
Mike Tyson/Mr. Dream in the NES Punch-Out!! has an uppercut that is a one-hit knockdown. For the first ninety seconds of the match, he uses it exclusively, so if you're not good at dodging it, you are completely screwed. On the other hand, if you manage to dodge every single one, he'll never use it again. To clarify: He does occasionally use that attack, but it's no longer a one-hit KO, thankfully removing the main That One Attack factor.
Several boxers have at least one special attack that can be difficult to dodge or counter at first, such as Bald Bull's Bull Charge (also an instant-knockdown attack), Super Macho Man's Super Spin Punch attack (which is another instant-knockdown attack), Mr. Sandman's Dreamland Express, or King Hippo's Twin Smash Combo.
Devil's/Angels laser beam in Tekken 2, also Jinpachi's fireball attack. Both can be dodged if you can see it coming though; Jinpachi's fireball can even be low parried(!).
Jinpachi's "stun palm". He creates a wave that stuns the character for a minimum of 3 seconds. It has priority over every single other action in the game, coming out as fast as a jab. If you're jumping or even just lying on the floor after a knockdown, it will reset you into a standing stunned position. It can only be blocked low with proper timing. Simply put, it makes any match against him purely luck based, as you can only win if he takes pity on you and decides not to use it.
Unknown in Tekken Tag Tournament 2 has the Mizuchi Claw move. It involves her summoning a portal from the ground, which traps you in place and causes a large hand to appear from the ground and splat you, forcing you out of the arena with a pixel of your health and your partner in. On Solo characters, it shaves off 50% health; this can be much worse depending on your skill level because she has an inclination to use this move over and over, which means certain death if you can't sidestep. That's not even taking into account her batshit AI and plethora of other cheap moves.
I-No's Megalomania in Guilty Gear XX and follow-ups. If any part of it hits, the whole thing hits. It comes in three patterns, and she can freely Force Roman Cancel between them to throw you off.
However, even Megalomania(which was originally a boss-only move but was eventually made playable due to being fairly easy to dodge with the right timing.) must bow to Boss-Dizzy's Wings of Light. Like Megalomania, Wings of Light consume the burst gauge instead of the Overdrive gauge, making it available from the start. The difference? Wings of Light has three different effects depending on the distance between you and Dizzy. If you are on the opposite side of the screen(max distance) a Pillarof Light falls on you, either dealing 3/4th of your health if unblocked, or 1/4th if blocked with Barrier. The second, if you are at an average distance, consist of a giant laser beam which turns around on the screen with Dizzy at it's center. Despite appearance, it is just fast enough to be completely undodgeable, and it is either an instant-kill(if unblocked) or deals roughly 1/3-1/2 of your health if perfect blocked. The final effect, if you are close to Dizzy(Like, say, you were attacking her when it started, or she dashed into you to put you into a corner), you die. Instantly.
Also, Accent Core gives us Boss Order Sol's Flame Distortion. It's basically Sol's Dragon Install except on this one the boosts are so humongous that he can close in from full screen in no time to counter your moves, and he also has infinite charge gauge, as well as auto-tension gain. His moves become so fast and strong that he can take off over 70% of your life in a single attack, because he's fond of his supers' invincibility frames. If he goes for Dragon Install Sakkai (which he can easily combo into), expect it to kill you.
Three words: Shun Goku Satsu. Final Bison from Street Fighter Alpha 3 also has a super fast, extremely damaging variant on his usual Psycho Crusher called Final Psycho Crusher.
Luckily, there are two tell-tale signs that he's about to use the FPC (in the PS One port, at least): Once his meter is filled, if he either teleports to one side of the screen or uses his diving attack out of the blue, it's coming next, no questions asked.
The King Of Fighters' bosses all have at least one of these. Rugal has Genocide Cutter and Gigantic Pressure, Goenitz has his spammable Yonokaze projectile, and Orochi has his screen filler super.
Magaki in XI gives us his fireballs. At times they fill the screen, and the blue ones are one-third of your life if they hit. Apparently someone confused The King of Fighters with a Bullet Hell.
Surely we can't just leave Rugal's Genocide Cutter as a passing mention. The move, in '94 anyway, has ABSOLUTE INFINITE PRIORITY and does the highest damage of any move in the game. God help you if Rugal has a full bar of meter. And on the subject of this series, Igniz's qcf+ P whip attack is an infinite. It can be done eternally as needed to empty your lifebar, and what's worse is he can also do it to set up for Brutal God Project, his very fast instant kill. In fact, he can do this without setting it up and you probably won't be fast enough to block it.
Krizalid, the final boss of '99 and essentially the "Rugal" of the NESTS Chronicles, has Typhoon Rage, which might possibly be in a league of its own. Not only does the damn thing have a large hitbox, but, much like Genocide Cutter, the move has priority over virtually everything, does ridiculous damage even on block, can juggle easily, and fills up Krizalid's meter absurdly fast (doubly so if you decide to guard against it). It's telling that, in 2002: Unlimited Match, Typhoon Rage makes Krizalid a bigger threat than every other boss in the game—in a game filled to the brimmed with SNK Bosses, including Omega Rugal and Igniz—barring Nightmare Geese. That's not even getting into his bag of other dirty tricks. One move alone, and he's already the second most broken character in the game.
Geese Howard's counterthrow in Fatal Fury. If you try to hit him with a direct attack, he can throw you. This includes jumping too close to him. There's also his Raging Storm in later games, which is often used the first frame of your forward jump.
Dead Or Alive 4. Alpha-152. Okay, got her... GOT HER... NO! That stupid attack where she grabs you, knocks you down, then smacks you across the face a few times which removes 70% or so of your health! Resist... urge... to... toss... 360... out... window.
Ragna The Bloodedge has a Awesome, but Impractical attack called "Devoured By Darkness" which is unblockable and damaging, but balanced by a requiring a lot of Ragna's super meter, having to go into his Deadly Upgrade Blood Kain state to use it, losing said Super Mode after an (attempted) use and being a close-range grab. Any semblance of balance goes out the window for his True Final Boss form Unlimited Ragna, who can use Devoured By Darkness nearly at-will to blow away 70% of your health and massively heal himself. Also, it doesn't remove Unlimited Ragna's Blood Kain.
Hazama's Serpent's Infernal Rapture. The damage isn't that insane - the problem is that he will use it on you the first frame you are open, and it knocks you flying into the air, totally disrupting your combo and setting him up for one. He can, and will, even pick you off with it between your attacks.
For a while the Street Fighter series was in love with these. In the Street Fighter Alpha games Bison used a full screen psycho crusher that would probably end up losing the match for you if you didn't block it. Gill from Street Fighter III had both a full screen nuke AND a self resurrection; fortunately Gill's attacks were interruptable, if you got to him in time.
The Hadoken from Street Fighter II was close. On harder difficulties, Ryu would happily fire a constant stream to chip you to death, and if you time the jumps poorly, he'd take you out of the air with a Shoryuken when you got close enough.
Balrog from Street Fighter II had two of these in his dashing punches. If he spammed them for long enough he could kill you through block damage alone with you having no defence unless you were playing as Ryu or Ken and your dragon punch timing was impeccable
In Dead Or Alive 2, the Tengu can use a wind attack. It can knock you over, do a large amount of damage, and worst of all, is the only ranged attack in the game.
Magical Girl Lyrical Nanoha As Portable: The Battle of Aces has a few of these. Hayate's - and by extension Material-D's - basic attack is a spammable energy-ball thing that, once you're in range, can pretty much lock down the enemy until you run out of mana. Vita's Swallow Flier with its five homing energy balls is hard for most to swat out of the air outright and she can whore it much more than one can usually dash away from it.
One of the biggest ones is Phoenix's"Dark Phoenix" mode, which restores her to full health with a buttload of stronger, projectile-launching attacks and a weakness (her constantly-degenerating health bar) that can be compensated for with relative ease. The uptick is that it's a Level 5 Super, so you'll know it's coming if your opponent never touches their Super meter (and if you can kill Phoenix before the meter reaches Level 5, you'll never see it).
Sentinel's "Strong" regular attack is a plasma beam the length of the screen. The easiest projectile to use in the game, and therefore the most commonly spammed.
Akuma is made of this. Most egregious is the Zankukyaku, a ramped up version of Ryu's Tatsumaki Senpuukyaku. Note that while both attacks hit multiple times, Akuma's does more damage, which along with the Gohadouken, Goshoryuken, and the returning Shun Goku Satsu, combine to earn him the reputation as one of the most feared and hated opponents in the game.
Galactus has one attack where he shoots Fricking Laser Beams from his eyes and fingers. Cannot be avoided unless you have a character that can fly over it, is a One-Hit Kill if not blocked, and takes away about 3/4 of your health if you do block it.
No list of irritatingly potent attacks from MvC3 is complete without Doctor Doom's Hidden Missiles assist. When called, Doom will fire missiles he likely put there some time ago. The annoying part is that the missiles fire upwards, arc down, and then home in on their target. Oh, what's that, you just started a combo you spent months practicing? Nope, you got hit by a stray missile, then the rest hit you and your opponent has just got you in their own combo, your character is going down.
Gantenbain's warping kick in Bleach: Heat The Soul 6. He warps into melee range and kicks you in the face. This attack has very little warning and is extremely difficult to dodge. Some of Szayel's heavy attacks are similar; he spawns a Giant Mook to attack you, except those moves have even less warning, and one of them can hit twice.
Arcana Heart 3'sFinal Boss Ragnarok has an attack that fills most of the screen with unblockable pink lasers. Hope you've mastered homing attacks to dodge it. Worse, it also gives him nearly a full second of total invulnerability in a Time Limit Boss fight.
The Final Boss of Tatsunoko Vs Capcom, Yami, has an attack that he uses during his first form where he lets out a red forcefield. It breaks guards and steals a special meter from you, and it's damn near unavoidable if he's in the center of the screen.
Any S-rank ability in Soul Calibur IV could qualify, but the worst is Auto Impact S, especially when combined with Impact Edge, Impact Heal, or both. It allows the enemy to randomly get Guard Impacts (thereby interrupting your attack and making you vulnerable to a counterattack), even if they do nothing that would merit one. At S-rank, it happens a lot. Impact Edge hurts you when you get Impacted, and Impact Heal restores health on a successful Guard Impact. Combine them for maximum frustration. It's also worth noting that only the computer can have S-ranked abilities.
Nightmare's Critical Edge is also That One Attack in the sequel, Soul Calibur V. Unlike many of the Critical Edge attacks, it can outright counter an incoming move instead of interrupting it, so you're going to be eating it unless you were blocking before he released it. Also, unlike most Critical Edge moves, which tend to do 25% or so of the health bar, Nightmare can devour 75% of your Health with this one attack and go on to use his multiple options for punishing downed characters.
Elysium's Critical Edge as well. It's pretty much a machine gun that fires invisible bullets. And if it hits you while you're on the floor, it causes you to levitate so you can be hit by her other attacks easier.
Gradius III's lava stage boss explodes into pieces upon dying. Pieces that will kill you if they collide with you.
In The Hunt'sFinal Boss has two phases where it only uses ONE attack. Unfortunately, said attack resembles something from a Bullet Hell: it generates a minefield of indestructible red mines that absorb your shots. Made worse is the fact that you have a large collision box.
The House of the Dead III has The Fool's final attack pattern, in which he jumps from one side of the cage to your side, swiping you in the process. To prevent his swipe from hitting you, you must hit his remaining claw 6 times in what little time you have. Now, your gun has 6 shells. If you miss even ONE of those shots, you will fail because it takes too much time to reload. Oh, and did you bring a second player with you? Well, now you must hit him 12 times, or 6 shots from each player. Which means if the other player is not very good, or is some dumb kid who is fooling around, you are royally fucked. Even if all of your shots are spot-on.
The Magician from the first and second games switches from fireballs to hard to counter melee attacks in the second and fourth phases of the battle. It's hard enough to shoot his weak spots, but it's worse when he attacks so quickly.
From Hellsinker we have Perpetual Calendars "Lunatic Phantom". It's a blue flame that fly around the stage in a semy random pattern at high speed. It also cannot be supressed meaning that if it catches up to you, you will either loose a life or burn an auto reject.
In the Shrine of Farewell we have Million Lives' "Innocent Clockwork". While it is perhaps the attack with the least amount of bullets in the game you'd be surprised at it's high bodycount despite it's simplicity.
Max300 and Maxx Unlimited both have crazy sections after the big pause in the middle. In fact, DDR has a metric, called Voltage, which basically just measures how difficult That One Attack is for the selected song.
Battle mode of the PS2 games can also throw modifiers at you in the middle of a song. One popular tactic for the computer to wield is putting 2 of the 4 arrows on Sudden, or putting every other beat on double speed. These are MUCH harder to read than they sound.
Healing-D-Vision has a 5-second run of 12th notes at 360 BPM. Have fun trying to Triple-A the song. Oh, and the run goes LDRDLDRD; normally these are handled by using the same foot for the L and R panels ("cross-overs"), but at this speed, that's a write-off; instead, the only hope is to exploit the design of the pad and brush the panels using the heel and toe from the same foot on different panels. Fun.
The streams in Horatio on Challenge, mainly because of the absurd amounts of Fake Difficulty in it. Especially egregious in the PS2 version, where the shock arrows are on EVERY GODDAMN BEAT OF THE STREAM.
Valkyrie Dimension has a slowdown near the end...which then becomes a massive stream at 400 BPM. Is it any wonder that it took months for someone to clear it?
The Challenge chart throws down another nearly impossible stream; this one goes at 480 BPM. To put this into perspective, Determinator below has 14.7 notes per second; this is 16. It doesn't help that, while In The Groove has a lot of really tough charts to get one used to runs like the one Determinator, DDR has very very few such runs, so when one does come along, it's an absurd Difficulty Spike that can only be completed by people who have played other games.
Sakura, even though it's widely acknowledged as the easiest 10 in the series, still has one, in the form of a slowdown to about 20 BPM. This is very, very slow and makes the incoming notes very hard to hit. And there's a second one at the end of the song, too!
Determinator is a fairly difficult but manageable song. Except for one little part that makes you move around the pad at the rate of 14.7 stomps per second. If you're not sure how fast that is, it is very, very fast. (Example here; the fast part starts at 1:16.)
Caprici Di Diablo's third guitar solo is even faster than the rest of the song. Dozens of other songs in Rock Band and Guitar Hero have their own That One Attack, but many can be faked through using star power. Unless it's at the start, like in Foreplay\Long Time, or a long "attack", like the drumming climax of most The Who songs, or there are two such attacks, like Green Grass and High Tides on guitar (like in many RPG examples, except you're guaranteed to get hit with it twice in a row).
Playing Free Bird in Guitar Hero II, one of the loading screens is "you're looking for "Gtr solo i" in Practice Mode."
Guitar Hero III had the infamous battle mode. You're in trouble if the boss hits you with Lefty mode, which mirrors the display of the notes. Lefties don't get off easy, they get hit with Righty mode instead.
For those who play on lower difficulties, Difficulty Up is a nasty one. If you get hit with it during one of the harder songs- especially the solo of "One" by Metallica- you will die fast.
The zig-zagging in Green Grass and High Tides is nothing compared to Satch Boogie on GHWT and RB [as DLC]. To borrow Guitar Hero 2's loading screen joke for Freebird, "You're looking for "Surf Solo" or "Guitar Solo 2A" in Practice Mode."
While we can't mention every DLC that belongs here, the song According to You is very, very this on guitar.
Can't Be Tamed is a pain on guitar as well, don't get fooled by the fact that it's a Miley Cyrus song, it's on the "Nightmare" tier for a reason. It's a particularly egregious example, because the song itself has no actual guitar parts(Harmonix charted the solo just for the game) and it starts off really easy, so you're most likely not going to expect to get nailed with a nasty solo section that gives "Tornado Of Souls" a run for it's money.
Walk up to any drummer that has seen the drums-expert chart to all of Coheed and Cambria's DLC and start singing "Cold as winter's guns of summer point and watch them run".
We cannot talk about this without mentioning the guitar solo from "Constant Motion". The first half is fairly easy. Then you get hit with the practically random strings of notes followed by a bunch of 23-note-per-second triplets. Eagh.
One of many keyboard charts with this is Roundabout by Yes. The whole thing is hard, but where does the shit really hit the fan? Why, in Subdued Section of course!
Many of the bits from BIT.TRIP qualify, but some of the worst are the bits that change back and forth from black to white from Void. If you don't get the timing down quickly, you will lose points both from missing black bits and collecting white bits, and you will fail ridiculously fast.
DJMAX Technika: Son of Sun (SP)'s end segment. GO GO GO GO GO—GAME OVER. Some people have even made montages of fellow players failing the song.
Also on SP difficulty: Your Own MiracleBullshit. Go on (Go on) / Pick those beautiful feet up off the—GAME OVER.
A.I. (TP)'s ending. It say something about how awkward the ending is when people who have cleared the Challenger Set still "spam" that segment. By the way, notice that all of the examples thus far involve gratuitous repeat notes?
Osu! Tatakae! Ouendan and Elite Beat Agents have their fair share of examples: the last section of "Shanghai Honey" on Insane (notes spread out all over the place and designed to mess up those who assumed Insane was just a mirrored Hard chart), "Jumpin' Jack Flash" and its infamous third verse (ridiculous clusters of notes with spinners interspersed), and, of course, the last 14 notes of "Countdown" (be prepared to go from full-health to fail in 2 seconds!).
If not the third verse of Jumpin' Jack Flash, the fourth and final verse is. A brutal segment where the game throws every beat trick it can think of, along with a weakened life bar (From the third section) that is dropping faster than ever. Miss any one of the notes haemorrhaged to you on Hard Rock and you are DEAD. Failing here is downright heartbreaking.
The Anthem in EBA has the final spinner for people trying to S Rank the song. The thing is 'Damn near impossible without spinning as fast as humanly possible.
The last sequence for the final boss battle in both games are a Kaizo Trap; failure to complete the last "chu chu chu" sequence as the boss is about to be defeated will cause an instant Game Over and you have to restart the stage all over again.
The second section of Report 2 Bonus in the first game. "Up down up down up down up down up down up down up down..." It's a solid thirty seconds or so of up-down finishing with a typical 3-Chu. Then after that, you get to do it again with Right left. Listening to the music helps you keep your place, but the sheer length of the commands can still throw you off it you aren't paying attention.
Push It vs. I Want Your Soul has a nasty stream of 16th taps all on the same track. And it's one of the faster mixes. Planet Rock vs. Busy Child also does the same thing, but it's shorter and makes up for it by having you hold a note at the same time.
Pretty much any time that pattern happens.
On Expert, Move For Me has a BRUTAL section with about 160 actions in 15 seconds (starts around 2:21 in the video).
The final song in Hatsune Miku Project Diva Second ("The Singing Passion of Hatsune Miku"). At first, you get a long stream of constant Os that feels like That One Attack, seeing as you're even greeted by an easier section directly after. Five seconds later, the game gets serious and you have to hit O eight times per second, doing it too fast gets you killed. This is still the easy part. And then when you finally feel like it's over... Well... Words really can't describe this. this is something you have to see. As pretty much standard, this is harder than it looks.
The first game has the similarly difficult "Disappearance of Hatsune Miku", which was clearly the predecessor for the way Singing Passion is played in the sequel.
Rank 2 in No More Heroes has an attack that instantly kills you. What does she do? She drops to the floor crying. If you hit her, or even get close to her, she instantly beats you to death. At no point is it hinted that this will kill you, and if you play the game without knowledge of this, YOU WILL DIE. To make matters worse, she can sometimes do this in mid combo. Even more aggravating is that sometimes she actually is crying (she only attacks if she left one hand on the bat), so you can get thrown off easily if you aren't watching.
Rank 4 of the first game, the boss has a near undodgeable spinning attack that takes a large chunk of health and can not be blocked.
Speaking of spinning, Mimmy in the second game. "YIPEE!"SLAP!SLAP!SLAP!SLAP!SLAP!SLAP!SLAP!SLAP!SLAP!
Rank 7 in Desperate Struggle can summon a dragon made of energy. This dragon will follow you very closely, and Travis can't dodge fast enough to escape it. And Rank 7 will still attack freely as it's chasing you! The dragon can be blocked, though it eats your battery like candy; it also has a tell: If the sky is dark it's still chasing you, if the sky clears it's gone.
Rank 1's second form is even worse. About halfway through the battle, he'll start teleporting around, attacking three times in rapid succession. In a game where you dodge primarily by rolling, this attack comes faster than you can roll. If you manage to get him down to 1/4th HP, he'll start spamming that attack and a series of three whirlwind punches that are equally difficult (read: impossible) to dodge. The worst part? Both attacks knock you back a considerable distance, and can send you out of the arena, one-hit-killing you. That said, the teleport punch is avoidable provided you have hair-trigger reflexes and know that the second punch will almost always miss if you dodge the first, leaving you free to dodge the third. The tornado punch? Nnnnot so much.
The suicide attack by the Egg Viper in Sonic Adventure, if only because of the horrid camera angle. Some of the Sonic Rush battles (and the Sky Canyon boss in Sonic Advance 2) have instant death attacks, or attacks which are nearly impossible to avoid consistently.
The Sonic Rush ones are very well-telegraphed, though. Probably the only hard one to see coming is the one where Eggman (or Nega) rams his giant robot's shoulder spikes into the stage at the end of said battle, mostly because you've never seen it before. The button-mashing on the Sonic vs. Blaze battle would be hard to see coming as well if it weren't for the mini-cutscene and the fact that one boss earlier used an easier version of the button-mashing gimmick.
The charging tackle Meta Ridley in Metroid Prime does when he's on the ground. It's not too hard to avoid at first, but later on, especially in Hard mode, he seems to be able to guess where you'll be. Cue frustration. In fact, physical attacks in general are pretty annoying in Metroid Prime as you may get cornered.
The whole reason the Boost Guardian in Metroid Prime 2: Echoes is That One Boss is precisely because of That One Attack. He's a piece of cake otherwise, even on Hard mode.
In Prototype, the Supreme Hunter can use the same tendril barrage you can, and it inflicts a terrifying amount of damage. Furthermore, depending on how chaotic the fight is, noticing the move being prepared can be extremely difficult, and there's no getting out of the way once it's been unleashed on you.
Dracula in I Wanna Be The Guy is already a bone-crackingly difficult Luck-Based Mission, but he has one attack that (even by IWBTG standards) seems programmed to screw you over. He shoots a single, homing Delicious Fruit at you. It's too slow to accidentally fly offscreen, hangs around long enough that you're gonna have to dodge it, and if he follows up with his fireball attack (which floods the floor with, well, fire), or those purple things are flying around, you're screwed.
In Castlevania: Order of Ecclesia, Dracula throws long streams of bats that bypass Mercy Invincibility and will shred your HP down to nothing in seconds if you get caught off guard. If you can avoid that, then it'll be the bloody soul steals out of nowhere, which do a lot to you and give him a bit more health back. Portrait of Ruin's bosses normally have a single attack that is much more difficult to work against than the others too.
Being the hardest of all Castlevania games, Castlevania III: Dracula's Curse gives Dracula's first form (of three) a fire spell that summons two spires on each side of your character and a larger spire directly targeting you, in which you have barely a microsecond to avoid. Sometimes the side-spires will spawn directly next to you, in which case you are fucked (see for yourself in the Angry Video Game Nerd's review).
Note the flame pillars will appear closer to you based on the distance between you and Dracula. So it could be very well a Schmuck Bait.
He also has one in Aria of Sorrow, where he rolls his scythe along the floor, walls and ceiling at high speeds. It too deals huge amounts of damage, and depending on where the player is standing in the room, it's anywhere from easy to nigh-impossible to dodge.
In Mega Man X5, the fight with Zero has him throwing nearly-full-screen Sword Beams that you have to dodge in sequence. Capcom acknowledged this by making this attack Zero's Level 3 Hyper Combo in Marvel Vs Capcom 3.
God help you if you're fighting Maverick Zero. His variation of that attack inflicts instant death or close to it, and if you should leave him at low health for too long, he will back into a corner and fire that attack continously until one of you is dead. Fun.
Bamboo Pandamonium's desperation attack in X8. Like every boss with such a move, he telegraphs it, but that won't help you; the punch he throws is sudden, fast, its hitbox takes up over half the screen, and deals an obscene amount of damage. On Normal and Hard, if you've not bought enough life gauge upgrades, you dodge it or you lose a character.
The attack is specifically designed to one-shot Ride Armour, which makes the fight much easier if you managed to manoever it to his arena, as it allows you to continuously pummel him while taking zero damage, until the Armour is inevitably destroyed. Better be confident in your reflexes if you're not in Ride Armour when that attack begins. Oh, and there is no Ride Armour when you fight him again in the Boss Rush. Hope you've got full Life Tanks!
Lumine's first form uses the desperation attacks of the 8 Reploid bosses, including the one mentioned above. However, there are two attacks that he modified; Avalanche Yeti's attack, which causes gigantic snowflakes that freeze you on contact to rain down, lasts a lot longer, and Lumine can still blast you with other attacks while it's in effect. And then Burn Rooster's attack, which engulfs the walls in flames, never wears off. After it hits the field, you can no longer wall-jump.
And going to the classic series, Wily's second form in 7 is often considered one of the most unfairly difficult fights in the series, and the majority of that reason is because of one attack that he spams constantly, summoning four differently-colored balls of energy that lunge forward at Mega Man three times. The attack is nigh-impossible to dodge (you have the best chance if Mega Man and Wily are on the extreme opposite ends of the screen, but it still requires perfect timing,) does anywhere from a decent amount of damage to taking out huge chunks of the player's life bar (especially if they get frozen by the blue sphere and can't break free fast enough to escape from Wily's follow-up attack) and is used every time he teleports. You know it's terrible when "Just get hit by one of the yellow spheres because they do less damage" is a perfectly reasonable strategy.
From Okamiden, we have Akuro's Wave Motion Gun attack. If it hits, not only does it deal out massive damage, but Akuro himself will be healed. The fact that it takes a while to charge isn't particularly comforting, as Akuro's Giant Hands of Doom can easily grab you and make you a sitting duck for the attack.
The final battle with Nelo Angelo (a.k.a. Vergil) from Devil May Cry has him throwing out his deadliest attack, summoning blue energy swords around you and using them on you like Reverse Shrapnel.
Hell Lusts from 3 have an uppercut attack. Admittedly it isn't too powerful, but it has ridiculous prioritynote How ridiculous? Death won't stop a Lust getting the move off., the demons love to use it while you're busy fighting others and they sometimes feint it by just doing the starting dash without actually striking, meaning prediction is difficult. Beholdthehorror.
Also from 3 Vergil's Helm Breaker in the last mission, specially after he says "you're going down". The move consists of him teleporting above you and striking you with his sword four to five times in a row, each from a lower height than the last. He may repeat this 2 or 3 times and since he is with his Devil Trigger on he will be recovering health the whole time.
He also has the abillity to project purple orbs to damage you, its fairly easy to dodge it in the first and second battle but on the third it becomes almost luck-based.
BunjiKugashira in the original Gungrave: "See Ya"/"Not So Fast!" Kicks Grave in the stomach —> shoots Grave while airborne = instant shield break and knocks off 25% of Grave's HP. This attack can KO you should the boss spam it (and he will). The fight even starts off with the boss using it, and it's very hard to avoid or see coming. It doesn't help that he's the only boss in the game that can heal.
The third phase of that flying claw boss in Frogger Beyond has an attack which elevates its difficulty to near-Luck-Based Mission levels. Basically, it's a leaded cluster of fireballs, followed by a fast fireball. Only problem is, each fireball hits a random spot, and there's no guarantee that you'll survive it. It may have a pattern, but since poor Frogger is a One Hit Point Wonder, one hit sends him to the first phase. This means it's nearly impossible to learn the pattern when it kills you every time. May the gods of random number shine on you if it glitches up and fires the attack out of the arena.
Phytops from The Legend of Zelda: Spirit Tracks prolongs gradually its thorned tentacle slash combo as the battle progresses. The ultimate combo is: moving its resting tentacles (to make Link's capture of the thorns to hurt it more difficult) while it shoots three series of goo drops, attacking with its left upper tentacle, then with the right one, and finally with both.
In Famous has the final boss Kessler. He can and will hit you with attacks that are almost impossible to dodge, and if he summons his giant copy images, well, best to take cover (but there isn't any!).
1: His support attack, which sucks you in and deals continuous damage
2: His soul-sucking attack, which does the same thing, drains SP and deals damage faster
3: Shooting laser bullets from his fists, which can't be dodged unless you're behind him and can't be broken out of except with a support, unlike the other two attacks. He can shoot up to eight at a time, and it can take off over 50% of your health if you aren't buffed up with defense-boosting accessories and/or Soul Pieces.
4: His Burning Attack, which freezes time and deals over 3,000 damage. If he does this after the laser bullets, you die.
Every Giant Mook in the game has at least one, whether it's the Doom Gigants' punching attack that can deal over 10,000 damage and send you flying a good distance back, the gigantic Shinigami with a nigh-unavoidable axe attack that hurts like hell, or the turtle Hollows with a splash attack that throws you up into the air.
KOEI has quite a few across its threesignatureseries, most of them handed out by high level characters or officers possessed of a situational super-buff.
Lu Bu, at all. His moveset is insanely powerful in just about every game he's been in since 3, but it's the throw from Dynasty Warriors 4 that really takes the cake. An unblockable multi hit throw with several officer and infantry mulching swings to tack on damage, followed by an overhead blow that occasionally sends players rocketing across the map, and more often sends their lifeless corpse into the next county, yet when you use it, its Too slow or The damage is too low. This move was taken out in 5...to be replaced with a faster, zero-telegraphing fire element dash that breaks block. Thanks, KOEI.
Pang Tong's Musou, in 4 and 5. This often involves him standing in one place and doing a lot of tornado air bursts around him, which often means he'll tack on at least three and often six good hits, and once again blow people off into the distance.
Gan Ning's Musou, 3 through 5. This attack is powerful, comes out fast, and sends Gan Ning racing across the battlefield at ludicrous speed. If he doesn't actually knock the player character down with the attack, the glancing blow that hits still takes off a good chunk of life, and leaves said character in a stunned state.
Zhang Jiao's...anything involving his fire element, but his fire based sweeping attack and Musou are fairly obnoxious due to increased damage and leaving players in a 'burned' state for a couple of annoying, vulnerable seconds.
Saika Magoichi's rifle blasts, especially his Musou in Samurai Warriors 1, which was unblockable for most characters (as 'bullet block' was a rather rare skill). Only his slow attack speed kept him from Game Breaker status.
Ishikawa Goemon's spinning attack with his mace goes on forever, and it's just fast enough that each hit juggles. Thankfully, he doesn't appear too often in normal gameplay.
The same can't be said for Maeda Keiji, who gets a block breaking area of effect ground pound and a brutal multi-hit Musou attack, and happens to turn up in quite a few story modes. He also shows up on his Cool Horse Matsukaze most of the time, so there's no running from him.
Orochi's moveset, notable his Jumping Fireball that breaks guard, Fire Elemental, and juggles, and anything with relation with Dark Explosion(Air Charge and Charge attack) which is just as broken when you use it yourself, justified as he is the end boss to a Massively Multiplayer Crossover.
FireMan has two; his regular attack which is only dodgeable with good slide timing, and takes off a good chunk of your health. And when his HP gets low, he periodically bursts into a pillar of flame. If you're near him, One-Hit Kill without the Heat Armor, and an absurd amount of damage with it. That's right, the first boss of the game has an instant-death move.
Zero has an attack where he lets loose an energy wave that takes up the whole screen and does 300 damage, a possible reference to the original Zero's Sword Beam attack mentioned above. God help you if you didn't pack an Invis.
Sonic The Hedgehog 2006: Silver's psychokinesis. He grabs Sonic/Shadow and slams them into a wall or tosses them into the sky. When the attack starts, it cannot be broken out of. Sometimes he'll use a follow-up attack that ignores Mercy Invincibility and is an instant kill. If you move forward and not to the sides at the beginning of the battle (with Sonic, at least), he runs up and uses it to one-shot you.
Assassin's Creed: Enemy Counter Attacks are pretty much impossible to predict and a free hit for the one responsible. Best hope no one takes advantage of Altaďr getting laid out.
Custom Robo has the Waning Arc and Waxing Arc guns. Each one fires four shots that can go around walls, and have slight homing. It really hurts if all four rounds connect. Very late in the game is a Dual Boss battle that utilizes both of these guns, in a stage with shifting terrain.
Chronoforce of Megaman ZX Advent has an attack where he swims into the background, shoots homing icicles at you, then reverses time to make them unexplode and fly back to him. If you didn't memorize where the icicles went you will get hit at least once as they rewind.
Another attack of his shoots icicles in roughly a 90-degree arc, with holes in between each icicle. However, on Expert Mode, he shoots off an extra set that goes in between the shots of the first one, making it nigh-unavoidable. Also, because you're playing Expert Mode, Chronoforce will have a permanent Time Bomb active; ergo, all his attacks move twice as fast as they normally would.
Just about every enemy in Dark Souls can be lethal if one is not careful, but there are several enemies with attacks that amount to a one-hit kill unless - and even if - Button Mashing is employed. The Hellkite Dragon in Undead Burg has four variations of his Breath Weapon that will reduce most players to cinders in one go, the Ents of the Darkroot Garden give a whole new meaning to tree-hugging, and the Mimic enemies look like ordinary treasure chests until opened, whereupon they proceed to messily devour the player.
ScoreDoom, a standalone Game Mod for Doom'. Its custom boss or miniboss monsters have at least one. Here are several egregious examples:
The Annihilator's homing missiles deal heavy damage, and are really hard to dodge, even in wide-open spaces (especially painful if said areas lack cover).
The winged goat demon Azazel's "stunned" state will make him shoot out ground-hugging fireballs that can rip through you, dealing incredible damage in a short amount of time. The fireballs are really fast as well.
The Demolisher's BFG cannon can outright obliterate you on a direct hit; however, he sometimes fires two shots, with the second one likely to finish you off; on top of that, the twin super gattling guns can shred you twice as fast if you don't hide.
Hellsmith's three-way explosive fireballs may as well be a One-Hit Kill on a direct hit, since each of said fireballs split into multiple explosions as well.
Every single one of Moloch's attacks are brutal, especially the hell grenades (very tough to dodge in tight spaces and deal massive damge) and nail barrage (these blaze through the map and rip through you for pretty large damage, and they rebound too).
Scourge's homing missiles can instantly kill you on a direct hit, and they're pretty fast to avoid as well. What's worse? He launches them in three sets of two. There's also that flamethrower attack of his that has a decent range but can quickly empty your health in seconds. Ouch!
The Dark Cardinal's homing energy ball nova attack is really annoying considering the mini fireballs home in on you and the attack goes off every time he flinches.
The Terminator's plasma grenade attack will total your health and armor on a direct hit, and it does severe damage if you're in the blast radius. It's a nightmare to dodge in tight spaces.
The Pyro Demon's teleport explosion attack is not only extremely damaging (splash damage ahoy) and a huge pain in the ass to avoid, he tends to do it pretty frequently sometimes. Mitigated somewhat in that he sometimes does it anyway even if you're not on the same level he is and he can't get down or up from there.
Thamuz's hard-to-avoid homing plasma ball can take you out instantly as well if it hits (that's without armor in this case); the ring of fire attack makes him invincible until he finishes the attack by sending the ground-hugging flames out (which only go straight, thankfully)
Also, Smokers on a level with holes you go down but can't go back up. Three teammates drop down, and the fourth is snagged before they can follow.
Hunters and Jockeys are also the bane of the slow ponderous player in these situations too. Second chances are rarely given among survivor players and most players who don't "get with the programme" the first time around and fail to jump down the right hole at the same time as the rest of the team are often summarily booted from the game if they get pinned/snared and become unsaveable.
Likewise for infected players, it is extremely difficult to pin/snare a survivor player and kill them before their buddies shoot you and rescue them (you are vulnerable to other players when pinning one and cannot move until your pinned target is dead). Therefore pinning/snaring a slow, clueless survivor player who didn't jump down the one-way hole at the same time as the rest of the survivor team is seen as a Crowning Moment of Awesome for the infected side and a benchmark by which to measure a player's skill as an infected.
Anything from the Tank. On Expert, both of his attacks will incapacitate you in one hit, and he's scarily accurate with the cement thrownote If you are facing against an AI Tank, change directions at soon as he throws and you can usually dodge the rock throw. On any other difficulty, one of his punches sends you flying, which can range from being a minor nuisance to sending you flying off a bridge/rooftop to your instant death, and the developers love putting instant death falls on finale levels, the only place where you're definitely running into a Tank. And you don't respawn during the finale event. Punching cars/debris counts too since it's another instant incap, regardless of difficulty.
Any attack in the game that damages also causes flinching, the Common Infected will reduce your speed to nothing if three or more are hitting you at the same time.
For anyone playing as the Special Infected, the Survivors' melee attack will stagger you long enough for them to move away and kill you, or they could kill you using just the melee attack if they're feeling sadistic, which most people are in Online Versus.
It gets even worse for the Tank: if your Tank dosn't have access to cars or cover to get to the survivors, the survivors will simply shoot the Tank player from a distance. Each shot causes flinching which will slow the Tank; with all four survivors wielding machineguns in a wide open area without any cars to throw, the Tank usually dies in seconds when survivor teams do this.
One attack from survivor players annoy the hell out of Tank players: Fire. If they hear a Tank appear, survivor players will use their molotovs as soon as the Tank player is in their sights or shoot nearby gas cans as a substitute. Once caught on fire, the Tank will keep taking damage until it dies, frustrating the infected team to no end. If there's any water nearby, then you're not as screwed.
Borderlands has the Roid Rage Psycho's Grenades. The boss seems easy and it's child's play to snipe his overly large head. And then he throws a grenade that will completely destroy your health and shields if it hits, leaving you open for him to kill you. To make it worse, he has a spread mod, so every single grenade will spit up into 6.
The Destroyer's shockwave attack. It's not very damaging, oh no. There are two issues: First, it pushes you out of cover, so it can get you with it's other attacks (Plus it's a pain to keep running back to cover) and two, prepare to throw your controller against the screen if you happen to be even remotely close to the edge when he uses it.
Wilhelm in [[Video Game/Borderlands2 the sequel]] has one. There's a train car in the area you find him...he comes out from underneath the train car and throws it. If you're standing near it, you die. You don't go into Fight For Your Life, you die.
In Crush Crumble And Chomp, a single shot from the Mad Scientist will cause the monster to gradually slow down (simulated by giving the player fewer opportunities to enter commands). This eventually proves fatal as the humans' attacks gradually overwhelm the monster. Similarly, moving into a space with a power plant results in an immediate game over.
In Angband, Ancient Multi-Hued Dragons and Drolems are notorious for killing players who descend to 2500' without poison resistance. Players without it will take 800 HP of damage from a single breath. From off-screen.
Agility in Pokemon Mystery Dungeon, especially in Monster Houses. Doubles the speed of every enemy in the room (they all get to go twice per turn), giving them more than enough time to wreck your party without you being able to counterattack. Even worse, the user of Agility is also granted a second turn, letting them 'use Agility again'. And if it's used twice? Quadruple speed.
Moves that hit all opposing pokemon, like Discharge. Wonderful when you're using it, ungodly painful when fighting against it, and an enemy manages to hit you with 3 or 4 of them before coming into range. The worst variation is easily Silver Wind (used by Venomoth/Dustox/etc), which not only hits you from all the way across the room, but also has a chance of raising all the opponent's stats, INCLUDING SPEED. Getting through dungeons filled with Silver Wind users turns into a Luck-Based Mission.
The Grudge Trap is That One Trap. Trip it, and every Pokemon on the floor is warped to where you are and given the Grudge status. In other words, when they go down, it drains the PP of the move you used to finish them to 0. Unless you have Warp Orbs/Seeds or Max Elixirs, you will die very quickly.
In The Binding of Isaac, there are many attacks that are incredibly difficult to dodge, especially if you're playing as a slower character. However, one that stands out is the attack used by the Leapers. They hop around the room like their lesser cousins, Hoppers, until they leap so high they fly off the screen and crash down near your character, sending out a fast blood shot in each cardinal direction. This gets very deadly when there are multiple Leapers in a room. However, far more devastating is the version of the attack used by Peep, where twelve urine shots are fired very quickly in a radial pattern, then eight more are fired right after.
In FTL Faster Than Light, boarding drones are one of the most dangerous things you can encounter. They bypass all shields except Zoltan Shields, never miss, and punch a hull breach into whatever room they enter - and that's all before they start attacking. They have as much health as a Rockman and an immunity to suffocation, so killing them is a major pain. And if you kill one while the enemy's drone control is online, they'll just fire another, which will punch another hole in your ship. Even if you can take the drone control offline, you still have to destroy the drone itself and repair the hull breach. The only good thing is that a Defense Drone mk1 can shoot them down, but they tend to fire so rapidly that they'll get by a drone fairly easily. Oh, and the Rebel Flagship uses these in its second form.
Drone Swarm. When it happens (and you do, thankfully, get warned well in advance), the Flagship launches about eight drones, most of which are beam drones. If your shields drop for even a second, the beams will slice your ship to ribbons, and if it takes out your evasion or shields, you're probably already done for.
Bleach: The 3rd Phantom: Sennen Hyourou. It deals a medium amount of damage, stops you from moving or attacking, AND lowers your accuracy and evasion. Did I mention it can hit the 4 squares around its target, too? That means MORE characters that get affected by it! It doesn't help that Hitsugaya has to be in Bankai when he uses it, so you'll take even more damage that isn't connected to that attack (In Bankai, anyone within a two-space radius of Hitsugaya takes damage and can be potentially frozen, lowering accuracy and evasion.)
It's not an attack, but Absolute Defense is too horrible of a move to not mention it. A character with this will randomly (much more often than not) take single-digit damage from ANY attack. Yes, even Co-Op attacks. A lot of bosses in Kisuke's Tower have it, and it is extremely frustrating.
Fire Emblem The Sacred Stones has the Silencer skill. It is the reason why Assassins are almost never seen as enemies; half the chance they have of landing a critical hit becomes a chance to instantly kill the other unit. And there is no defending against it; when the Assassin sprite flickers, you're losing someone.
Fortunately, no Assassins appear as enemies in Sacred Stones. The only occurrence of an actual assassin as an enemy character is in Blazing Sword, and depending on the path you take, you might not even fight him. (He shows up as a reanimated corpse during endgame, though, and you do have to fight him, but since he and every other boss on that map have 0 Luck, this isn't hard.)
As of Fire Emblem: Awakening, enemy Assassins do exist. Specifically, you can face actual player-trained Assassins in Streetpass battles! Which means they'll most likely have capped Skill and thus a ridiculously high Lethality chance. Oh, and it gets better: due to the new class-based skill system, even non-assassins can have Lethality now. Oh, and it now works for ranged weapons (Assassins can now use Bows) and even magic!Have fun!
Another example would be the Hel spell in Seisen no Keifu. Basically, it's an HP To One attack. In a game with Final Death. And unlike Eclipse in the GBA games, this one can actually hit you. And if your HP already is 1, it kills you. Did I mention the enemies with this spell come in groups??
Some ROM hacks bring their own horrible weapons to the table, such as GhebSaga with the Demi Lance. It hits for 1/2 of your maximum health, but has the Brave effect, meaning it ALWAYS attacks twice. It also can be thrown for a ranged attack. The only thing that doesn't make it completely rage-inducing is the fact that its accuracy isn't the greatest, but it's still able to kill you instantly.
Bane, used by Whispers in FEGirls. All Whispers have the Kard, which allows for critical rates to reach the cap of 255%, and Bane has a (critical chance / 2) chance of activating on each attack. Just pray there aren't any other enemies around.
Ashera's Judge attacks are grossly powerful at 60 Mt apiece, and they're able to hit twice. If it targets someone like Gareth (who is equal parts Eleventh Hour Superpower and Mighty Glacier), it could very well spell death for them.
Counter in Fire Emblem: Awakening. Any damage taken at close range is returned to the person who inflicted it in full, and this skill always activates on a close range attack.
One thing that makes Lunatic+ so hard is that enemies will almost always have a skill like Vantage+, Luna+, Hawkeye or the aforementioned Counter, or any combination of the four from as early as the Prologue. Vantage+ makes it so that the enemy always attacks first, Hawkeye means their attacks will connect (except on a lucky Dual Guard), and Luna+ always makes their attacks as strong as if your Defense/Resistance was halved.
Dragon Rage early on in Pokémon Conquest. Like in the main series, when it hits it does 40 damage regardless of enemy type or relative strength. It becomes a bit less of a hassle in long campaigns when your Pokemon generally become able to take two or three hits from it, but it's a total Game Breaker before then.
The Titan Dweevil's Monster Pump in Pikmin 2. It shoots balls of water everywhere and has incredible reach. If you're not paying attention to both of your pilots you could potentially end up with your entire army drowning.
Stun grenades from Jagged Alliance 2. Everyone within the area of effect, which is quite large, has their stamina bar take a huge hit that will almost certainly render them unable to perform any action during their next turn. And if you're lucky, some of them will have recovered by the turn after that. You can mitigate the worst effects of this one whilst outdoors by not letting your team get bunched up, but heaven help you if you run across a Mook with one of these whilst trying to fight your way through a narrow corridor.
Plants vs. Zombies has Dr Zomboss' desperation attack, in which he drops a caravan onto six of your plants, instantly squashing them. Unlike most of his other moves, this one cannot be avoided. Thankfully, it is predictable (he only uses it once he is below half health, immediately after he gets back up from attacking). It gets used much more frequently in the "Revenge of Dr. Zomboss" minigame, where it becomes exponentially more aggravating.
The Destroyer from Mini Robot Wars merges two of Dr Zomboss' attacks and cranks it up to eleven. Its deadliest move has it open its mouth and fire out a Wave Motion Gun at two of your rows. Sure, you can move a few of your minirobots out of the way, but this attack will most likely destroy any non-defensive unit in the area of effect. Worst of all, this attack comes out without warning, unlike Dr Zomboss' caravan!
Though several items and weapons in the Mario Kart series can be jarring and chaotic, both the Spiny Shell and the Thunder have gained notoriety for toughening the races for the players, especially the former for the first-place rider. Same reason why they're considered a Scrappy Mechanic.
The Quake in the Wipeout series, a super-fast wave that can travel the length of any given circuit. And getting hit with it makes you lose control and slow to a crawl.
EG-R's super weapon in Fusion, a set of drones that circle a car and fire constantly until either they run out of ammo or you die. Which one comes first depends entirely on whether or not you are at or close to full shield energy.
In Pure, the Disruption Bolt. It does no damage, but it causes one of many negative effects, ranging from the camera shooting in and out to your airbrakes being disabled. The one good thing about it is that it has a small chance of instead activating the autopilot.
The 7-10 split in bowling. Trying to turn one into a spare? GOOD LUCK. The U.S. Bowling Congress used to give out an award for any confirmed 7-10 conversion in an amateur league.
Magic: The Gathering has a whole "restricted list" in Vintage and a "banned list" in other formats. Every last one of those could be That One Attack. Three cards even annoy the judges so much that they're banned in Vintage: Shahrazadnote Creates a game within the game, Chaos Orb, and Falling Star. There are other Vintage-banned cards, but they use ante, a mechanic involving changing ownership, something never done in tournaments.
The Yu Gi Oh Trading Card Game has several, but the effect of "Chaos Emperor Dragon— Envoy of the End" takes the cake. For 1000 Life Points, the player can send every card on both sides of the field and in both players' hands to the Graveyard, inflicting 300 points of damage per card! You can see why the Chaos Dragon was quickly banned from competitive play. "Cemetery Bomb" has a similar effect, though not as devastating: It does 100 damage to your opponents' life points for every card in their Graveyard.
In Homestuck, the bearer of the queens' rings or the kings' scepters are granted a number of powers:
The most commonly dangerous one is Red Miles, which is the Black Queen's signature attack. When used, the Miles will hunt down anyone or everyone on a planet and stab them through with a One-Hit Kill. If this is done to a Genesis Frog from outside the universe it embodies by an especially powerfully prototyped ring, it can kill off that universe after impaling everyone and everything in it. The only way to escape is to either flee the universe or to be travelling so fast that the miles can't track you. This attack is why it is imperative not to allow the Black Queen's ring to fall into the hands of any of her agents.
In the Trolls' session, Feferi prototypes her sprite (and thus all the monarchs) with a city-sized Eldritch Abomination whose psychic scream can kill off every member of her species in the galaxy except for her and the Empress she's in line to replace. Unfortunately, the Black King of their session gains this ability, requiring a truly stupendous number of alternate timeline clones of her group's strongest psychic to nullify.
If you're not prepared for it, the spell Harm from Dungeons & Dragons can qualify. A successful shot will reduce you to 1d4 HP regardless of how many you have. (Granted, it can be resisted, saved against, interrupted, countered, etc.) And there's the arguably-more-annoying reverse spell, Heal, that can restore a boss to full health from whatever it happens to be at. This is precisely why Harm and Heal were capped to 150 points of damage or healing in 3.5 Edition.