Bad Breath from every Malboro variant ever. Causes all status ailments, potentially leaving your entire party paralyzed, bleeding to death, and attacking each other from a single attack.
Final Fantasy X gives us Great Malboros that uses this as its opening gambit. Wouldn't be a problem if it didn't also get "Ambushed!" every single time. With the characters now poisoned, confused, and blind, they will now constantly attempt to kill one-another only to miss and take poison damage. Frequently you will die without having been given a single chance to do anything.
Especially annoying since this actually makes your party worse as it gets better - if you have a high Evasion, your only chance to get un-confused - the Greater Malboro's bite - keeps missing.
Final Fantasy VIII comes close to this, coming in second as far as Malboro terror goes only because of the ability to run away.
Final Fantasy VII has it bad too. Sure, the Malboro doesn't get a free first turn in this version, but in this game it only attacks count as magic, so when it uses Bad Breath to put the entire party to Sleep (if neither of your party is equipped with a ribbon or a sleep protection), its other attacks damage you without waking you up, so you can just sit there and watch your slumbering party members die off one-by-one.
Final Fantasy XII nerfs it. It only causes Blind, Silence and Slow, but the game also has Putrid Breath, which has an even wider range of statuses (nearly all of them) and Curse, which gives you Sap (constant health drain), Disease (no healing) and Confuse. The game also has Cloying Breath, which inflicts Sleep and Slow. Also see Sporefall below.
Final Fantasy I. Astos. Rub. Instant death to a party member, in a game in which (in earlier versions at least) you cannot resurrect characters during battle, or even outside of a town (which is relevant because it's a long trek back to the elf village even if you win). Hope he didn't hit Fighter or White Mage.
WarMECH's Nuclear attack. Unless you've leveled up enough to be ready for the final boss, it stands a good chance of taking out any wizards in your party, and reducing your meat shields to a fraction of their hit points. If it managed to ambush you and used this attack in its free turn, just accept that some total party kills were simply meant to be.
It's not enough that Chaos, the Final Boss, averts No Cure for Evil. Oh no, he can manage to use the most potent cure spell in the game, which instantly restores all of his hit points. The only thing keeping him from abusing this and his One-Hit KO and Total Party Kill moves (of which he has several) to become impossible to kill is A.I. Roulette.
The imps from Final Fantasy II have a nasty habit of spamming Confuse XVI on your whole party. Unless at least half your party is immune to confusion, it's a crap shoot every time you meet them.
And by "lots" we mean instant death to your entire party unless you defeat four other tough bosses.
And if she uses it twice in the same turn, you're pretty much screwed.
Amazingly enough, this is a little better than the original Famicom version. In that, Cloud of Darkness used Flare Wave every round, every. Single. Round. It hits all four characters for 2000+ damage, in a game where, if you leveled up a character to level 50 with the best stat growth for HP, he might have 4500 HP. In order to have a chance of winning, you have to have two Sages casting nothing but Cure 4 (Curaja) every round on all your party members. And if one of those Sages goes down before you kill Cloud of Darkness...well, fuck.
Before Cloud of Darkness, there is Garuda and his "Lightning" attack. Crazy high lightning damage to the entire party; at the time you fight him, it's most likely three-quarters of your max HP. Even if you bring a party filled with Dragoons (his weakness) and use Jump right off the bat, there's still the chance he'll go first, use Lightning, and leave you with a party one hit away from death.
Even if he doesn't use it first round, you'll be praying he does the following round, because if he doesn't, when your Dragoons land, they'll get hit by Lightning. It's an extremely difficult battle because there's little you can do but keep jumping and hope that the turn order works in your favor.
Big Bang from Final Fantasy IV's Zeromus. Deals lots of damage, and any survivors suffer continual hit point loss. The Bonus Boss version of Zeromus in the GBA version, Zeromus EG, can do this move two times in a row.
In the GBA version, a glitch can happen against Zeromus EG, where his Big Bang gets stronger and used more often in a row as he loses life. If you use codebreaker to set your party's health to 9999, it won't save you. Once your damage starts to cause an integer overflow on him (healling him rather than hurt him), his next Big Bang will cause 9999 points of damage on the ENTIRE PARTY.
The DS version makes Meteor and Whirl into these. While in the original game, Zeromus's final phase Meteor did pitiful damage, this version's Meteor does damage comparable to Big Bang. In addition, his end phase now has Whirl, which drops all party members' HP to single digits unless they used Jump or Hide beforehand. Coupled with Big Bang's Sap effect, Whirl can end the battle instantly, and Meteor comes right after if anyone survives.
The dungeon that leads to Zeromus has the Blue Dragons' Ice Storm, which deals nasty damage faster than Rosa can heal; Red Dragons' Thermal Rays, which pretty much do the same thing; and Luna Dragon/Lunasaur, who casts Bad Breath... as an Area of Effect spell. In fact, Luna Dragon/Lunasaur is hardcoded to start one shotting your party members if the fight lasts too long: considering they wind up being confused and blinded at the same time, rendering them unable to hit themselves out of it, it feels more like a Mercy Kill when it does so.
Dr. Lugae loves to use reverse gas right when your caster finished charging up a big spell, so if your were going to use that aga level spell to "heal" your party, congrats, you just nuked them into the ground. Were you gonna try to nuke him instead? so sorry, you just healed him for half his health, nice job Rydia/Rosa.
Almagest from Final Fantasy V's Neo Exdeath and Neo Shinryu. It's Holy-elemental, which is practically impossible to resist, and deals absurd damage to your entire party, then drains the health of any survivors. The only way to survive it is to have a Job with a very high HP stat, or a Shell barrier active. And in the case of Neo Shinryu, even having both at once may not be enough.
Encircle, from pretty much any enemy that uses it (thankfully, not many of them). It erases a character from the battle, which means they're effectively dead, and it's impossible to reverse the effects of it once it's been cast (except by ending the battle). The only way to stop it is with the Aegis Shield, which only has a 1 in 3 chance of actually succeeding, and only on the character targeted by the attack; it's very unlikely you'll have four Aegis Shields. Oh, and one of the enemies with access to this move is Omega.
And in case Omega wasn't satisfied with Encircle, it can also use White Hole, an attack that does quite a bit of damage to one character and petrifies them.
Final Fantasy VI— Kefka's Forsaken isn't so bad on its own. It's a non-elemental AOE that's practically impossible to defend against, but doesn't do that much damage. The problem is that he loves using it right after his "Heartless Angel/Fallen One", which reduces everyone's HP to 1. Hope you remembered to cast Reraise— or had a Curaga/Lakshmi summon queued right after the Heartless Angel lands. Oh, and the only reason it does so little damage is because it's affected by magical resistance. If it wasn't, it would do even more damage than Ultima.
When you face Kefka, you line up your allies in twelve. The first four are your initial party, and after that, if you defeat one stage of the final boss with anyone dead, stone, or zombie, they will be replaced. Did we mention that the third stage of this boss likes to use a petrification attack as a final attack? (This is beatable: Just equip everyone with the right relic, but still...)
The MagiMaster uses Ultima as its last attack. Hope you used Reraise, which you can only get on That One Sidequest. (Ultima is survivable, but requires a lot of level grinding — more than you need to beat anything else). Or you could just use Rasp and Osmose to drain his MP, killing him while preventing the Ultima; or use the Palidor\Quetzalli esper to only kill the one that gives the final blow).
In the Advance remake, the Holy Dragon's souped-up form in the Dragon's Den will dualcast Heartless Angel with Southern Cross. That's a total party kill unless you used reraise, which is unlikely, since the dragon gives no prior warning to this combo. Worse, you have to trek through the entireDragon's Den again!
Sieze, used by the tentacle monster in Figaro Castle. It causes slow, and if a slowed party member is hit with Sieze, then the tentacle grabs him and leeches off his or her health, as well as taking them out of battle for a couple turns. And there's four tentacles, when you have three characters max at that point in the game. There is a way to counter it, thankfully; equipping Running Shoes will auto-haste your characters, preventing the tentacles from grabbing that character. Good luck figuring it out yourself, though.
The Goddess's Cloudy Heaven attack. It inflicts everyone with a count-down timer which up to this point most players know it means instant death when it goes off. Reraise/Life 3 should take care of that right? Except this one has a twist: it causes zombie, which is as good as dead but is only curable with Holy Water. If you try to Take a Third Option and kill the party member to null the countdown, they're zombied. If you cure the zombie status but that character dies still, they're zombied. The only thing that prevents the zombie effect from happening is if you're party is equipped with relics that prevent instant-death, not the zombie status effect.
Magnitude 8 from the Hades Gigas/Hill Gigas in Zozo. Does a good chunk of damage to the whole party at a time when you've got one magic healer on your team at best.
Sephiroth's Supernova from Final Fantasy VII, which deals 9/10ths of the party's hit points in damage and can inflict confusion and mute. It also takes a minute and a half to sit through. However, it can be noted that Supernova is a percentage based attack, so it cannot actually kill you... and it's kind of cool-looking, at least the first time he uses it.
There's also Bonus Boss Emerald Weapon's Aire Tam Storm, which deals 1,111 damage per materia equipped on the target party member. Since nobody mentions this little detail it almost always does maximum damage, and since it targets everyone, well... You'd better have Phoenix and Final Attack equipped. And if you know the trick, it becomes trivial to take out half of its hit points in retaliation. Still a Guide Dang It on the first play through, but one you can use to your advantage.
Carry Armor's Lapis Laser hits the entire party and is terrifyingly powerful. As you damage Carry Armor, it Turns Red and starts spamming Lapis Laser, eventually using it every turn. Even with Big Guard active, it tends to take over a third of your properly-leveled party's HP off.
Crisis Core has the Flare attack that easily deals a few thousand damage even through a MBarrier. What makes it worse is that you will meet enemy encounters with multiple Flare-users before completing half the missions, so you most likely won't be able to interrupt them all. Time to build your HP+ 999% and max Spirit materia.
Delta Attack is an attack used by the Movers, harmless-looking fluffy balls in the final dungeon. It involves them floating, following you and using consecutive thunderbolts to hurt you. If you don't roll around madly to avoid it the best you can, you will end up dying.
The bonus bosses of Final Fantasy VIII have some annoying attacks. First is Light Pillar, which instantly kills one party member with 9999 damage. This isn't too bad, you can fix that quickly enough with a Phoenix Down or the Revive command. They also have Gravija, which deals percentage-based damage. Can't kill you, but makes it easier to die unless you heal fast. There's also an attack called Megiddo Flame which does 9998 damage. The game assumes that by the time you're facing a Bonus Boss, you're good enough to have 9999 HP and a repertoire of healing spells, which is pretty much the only way to survive that attack. But the worst of them all is Omega Weapon's Terra Break. It is a more powerful clone of the Meteor spell, which randomly divides ten attacks across your party. Now, Meteor isn't too bad, if you're lucky, it'll hit someone with lots of HP or spread the damage out evenly enough that your party survive, and the ten hits don't do much damage anyway. But Terra Break is not like that. Terra Break is like a physical-attack version of Meteor, except each hit does upwards of 3000 damage, damage which is not mitigated by your Vitality stat like most physical damage is. Even if your entire party has 9999 HP at the time, without proper preparation, it is nearly impossible to survive. Your only options are to make your party invincible with items, or had everyone summon their GFs beforehand to absorb the damage. You can also cast Protect on the entire party to halve the damage of each hit, but that won't ensure that your whole party remains standing. Alternatively, assuming you have GFs that still know the otherwise useless Defend command, you can order your party to Defend against the attack, which will nullify the damage completely. And even then, you have to know where Terra Break comes up in Omega Weapon's attack sequence.
The aforementioned Light Pillar is not that bad when Omega Weapon uses it, as Omega has a set pattern of attacks and will at most use it once at a time in a predictable moment. Ultima Weapon, while weaker than Omega on the overall, will use it randomly, and it's much faster than Omega. If the A.I. Roulette decides it wants to spam it three times in a row, you've pretty much got an unavoidable Total Party Kill, unless you have invincibility on someone.
Omega Weapon also likes to use Lv5 Death. The maximum level for your characters in Final Fantasy 8 is 100.
Diablo's gravity attacks. It drains your parties health rapidly, especially considering you are probably fighting him early in the game, and he is pretty darn quick to attack again with his normal strikes, which WILL finish you off. The only way around this is to Blind him, but that always takes several casts to work, and unless you grinded Blind spells in a specific battle earlier in the game, you may be out of luck.
The magic spell Curse from the same game also has the same effect while adding in significant damage. Bonus Bosses Hades and Ozma use this spell (without warning in Ozma's case).
Ozma has Those Two Attacks. Curse is as above: harsh damage plus a grab bag of all the Standard Status Effects you haven't immunized your characters against. Meteor, however, turns the whole battle into a Luck-Based Mission, as it deals slightly random damage, but will most often inflict 9999 damage on all party members. Did we mention Ozma likes to cast Meteor followed by Curse? Enjoy.
Trance Kuja's move Flare Star is incredibly annoying. He can continuously use the move many times with others up his arsenal dealing heavy damage to the entire team, bound to have at least one party member killed from it. Even though the move itself is avoidable, it's still a very lethal attack.
High levelled parties can take advantage of the long animations the strongest attacks (including your own) often have by combining the Auto-Haste and Auto-Regen abilities. That way, even if the first attack leaves you hurting, the second will take so long to actually inflict its damage that you'll have healed (nearly) to full.
Seymour Flux's aptly named "Total Annihilation" will one-shot your party if you don't use Shell first. If you can't kill Anima in time, "Oblivion" will break you. Pretty much any attack that one-shots aeons is one of these, but if you're facing an enemy that does this, you're probably just using them for their Overdrives.
Sin's Overdrive Giga-Graviton not only takes the party out, but it takes out the airship you're on for an automatic Game Over, putting a fixed round limit (16 rounds) on a battle you basically have to start with magic only (Sin is out of range of physical attacks aside from Wakka's, which limits you to using magic or long-ranged Overdrives until he gets close enough).
Dark Yojimbo's Zanmato overdrive. Did you have a summon out? You live this time. Did you not have a summon out? Congratulations, your party's dead, and your Auto-Life crumbles like a biscuit hit with a hammer.
Evrae's Poison Breath will damage your entire party and leave you with a serious poison status that will probably kill in a couple of turns. Also, you don't have Yuna in this battle which means you can't use neither your healer or your Aeons to take the damage.
Sporefall from Final Fantasy XII's Elder Wyrm. Inflicts on the order of 8 status ailments with a large area of effect, probably hitting your entire party unless you really know what you're doing. If you're not prepared, by the time you've recovered from these ailments, it's probably close to casting it again.
Note that all of the status effects from Sporefall can be cured with upgraded remedies or Esuna, which you do have access to at this point...all of them except Oil, which you're likely to ignore the first time because it doesn't seem to do anything. What does it do? Makes you extremely weak to Fire damage. What's the Elder Wyrm's other favourite attack? Fireball. Boom, KO.
And the one for regular enemies is Curse— this one move can make any enemy into a demonic spider. It works by hitting your party—all of them—with a mana-free (so you can't silence the enemy or drain its magic), unblockable, unevadeable status bomb that inflicts poison, sap, confusion, and disease—that last one is exceptionally fun, as it means max HP is always equal to current HP, meaning a character cannot be healed while Diseased. Disease needs a special item or spell to remove it, and another spell to remove the other status effects. If a Diseased character dies, rezzing them leaves them with 1 HP and disease, yes, STILL in effect. Because Ribbons are stupidly, horrifyingly rare in this game, you will only be able to protect against ONE of these ailments—if any monsters (plural, they come in groups) who use this attack can be available long before protective armor is. Basically? If three or more of these status effects stay on your party for more than, oh, three seconds? Death. If you are caught without fully upgraded Remedies? Death. No accessories to protect against confusion? Death. Command priority unkind to you? We're so sorry.
Though as bad as that is, there is two small saving graces with that attack: 1)it can only hit each character in succession, even if it affects everyone in an area, and 2) the animation for curse precedes the actually status-inflicting attack. All you really need is one Ribbon, and once the game says the enemy used Curse, wait for the animation to start, jump into the inventory screen and equip the Ribbon on the character about to get hit. Once the Immune message pops up on the character, give the Ribbon to the next victim. Granted, this still relies on finding even one horrifyingly-rare Ribbon, and setting the Gambits so the characters won't die while you watch the animations.
Growing Threat is used by some bosses to double their level, and thus their damage output.
Zalera's Kill. Three guesses on what it does. Spammed often if you don't understand how the battle is to be fought. In addition to Kill, Zalera seems to be the math instructor from hell. Any spell he has is a level based disabler of some sort, and his ultimate attack is a group wide instant death spell. Don't worry, it won't kill you if your level isn't a prime number... which is the only way to not get hit by all of his other level-based spells. You can beat Zalera by just knowing not to be a prime, or a multiple of 3, 4, or 5.
Zodiark's Darkja, which blinds and does an instant kill. You can absorb the darkness, block the blind status, but you will have nadda for the instant kill effect. Luck will almost never be on your side after it is cast.
Chaos's Aeroja. It deals wind damage and confuses. Not so bad since your allies will snap out of it with a bonk to the head right? Normally so; except in Chaos's battle, you can't use physical attacks at all. So you can't snap yourself out of confusion if all three allies are confused in the fight.
Ultima's Holyja. It deals holy damage and causes Reverse. Ultima then casts Renew on your team shortly after Holyja (no charge time required) causing an instant kill. If Reflect is on your team when it happens...
Speaking of Ultima, any attack that causes Reverse, though Disease can be just as annoying. Reverse makes you a case of Revive Kills Zombie, while Disease is a No Sell on healing.
Yiazmat's Reflect and Renew strategy... if not caught, you can heal the boss of all of his HP. all 50,000,000 of it.
Any sort of barrier or paling that a boss may put up on himself. An impregnable defense that only goes down over the course of time? Enjoy your unnecessarily long boss fight.
By the end of the game pretty much any enemy that can cause confusion will be extremely dangerous. Your party members will be strong enough to effortlessly one-shot each other with physical attacks, so a single confused ally can wipe out the rest of the party in just two turns. In theory this should be more than enough time to cure thim - except that the command priority always gives a huge advantage to physical attacks. Even if you see an enemy casting confusion on a character and immediately tell both of the other two to throw him a curative item there is still a good chance that he will wipe them both out before they can perform the action.
Final Fantasy XIII has Merciless Judgment, employed by the final boss, Orphan. It's basically like Supernova, except it can kill you unless you have nearly full health or a sentinel on your team. Oh yeah, and it resets the boss' stagger meter.
There is also Dies Irae. The first form of Orphan tends to use this move when you're close to defeating it. It can be an instant Game Over if your party leader doesn't have full health.
The Adamantoises generally don't have attacks that don't suck, but the worst by far is Roar. It deals horrifying damage to ALL party members, and, worst of all, tends to inflict Daze on at least one party member. Daze prevents a character hit with it from performing any kind of physical or magical attack. If it lands on the healer or the leader, or anyone at all if the damage from Roar KOed some characters...well, you're screwed. Everything else the toises have can be dealt with simply, but the best strategy for handling Roar is to kill the monster before it uses it. Good luckwiththat.
Barthandelus' Destrudo. Total Party Kill unless you can damage him enough while he's charging, which is never hinted at anywhere. Granted, it takes forever to charge, and you really don't need to hit him that hard to weaken it, but woe be unto you if you figured the long-ass charge time was ideal to swap to a defensive paradigm to heal and reapply your buffs. Also, and even more infuriating, it resets his stagger meter.
Every attack used during the second fight with him. His basic laser attack can cause Fog or Pain, Apoptosis neutralizes any buffs and debuffs you've cast, Thanatosian Laughter devastates your party, and Cursega and Dazega for obvious reasons. The third and final fight with him is a damn joke, but Thanatosian Laughter is even more dangerous.
Dahaka's Diluvian Plague, which causes a whole host of status ailments and dispels any buffs you've cast. He also has several powerful elemental spells, the worst being Aeroga.
Wladislaus' Mounting Contempt. It first inflicts Deshell and Deprotect, and then hits the target with a terrifyingly powerful attack. If either of the status ailments stick, it's pretty much a guaranteed kill to anything but a Sentinel.
Orphan's second form's Temporal Hollow. Doesn't do much, dispels a few buffs and debuffs, and resets the boss' stagger meter...except said boss can't be damaged except when it's staggered...and its AI is set to use Temporal Hollow when you approach stagger...and you're on a strict time limit for this fight.
Vercingetorix's Wicked Whirl. If you're not in a Sentinel-heavy paradigm, Wicked Whirl will tear you up, and you only get a few seconds' warning to swap; even with Tortoise (3 Sentinels) it'll leave you in dire straights. It gets worse towards the end of the fight, when he'll start spamming it; he initially uses Imprenetrable Aura immediately afterwards (he's invincible, buffs and regens for its duration, but doesn't attack you; itself a candidate for That One Attack), later he'll keep attacking after using Wicked Whirl, and the rest is all down to luck that he leaves your party leader alone. Putrescence is also problematic, as it dispels the buffs of whoever it's cast upon.
Final Fantasy XIII-2 has its own fair share of annoying attacks, especially the often spammed debuffing attacks.
Sunder used by some Behemoths after they stand up. Usually by the time you meet these Behemoths, this particular attack is too strong for your party to survive without being taken to critically low HP, and even then the Behemoth can just cleave the rest of the HP away.
Proto Behemoths met in the Final Dungeon are actually harder than the Final Boss due to this attack being able to one shot your whole party, unless you are way beoynd the levels needed to take down some of the hardest optional bosses. The only way to have a fair fight is to kill it before it manages to stand up, which you probably can't do by the time you first arrive here.
In fact, even its regular cleave attack will probably one shot any party member the first time around.
Chaos Bahamut's Megaflare. If you're a bit banged up, this will wipe the entire party, and even if you're at full health, it still does horrifying Wound damage, slicing off up to a third of your party's total HP, unless you knew it was coming.
The Giga-, Tera-, and Exaflare combination attacks used by Jet/Garnet/Amber Bahamut put Megaflare to shame.
Oh man, the final boss fight is made of these. Garnet Bahamut's Anti Force dispels any buffs you try to cast (except Reraise). Jet Bahamut's Dying Sun has a very quick casting time and is extremely powerful. Amber Bahamut is probably the weakest, but its Apparition Ray is still not something to mess around with.
Caius' Chain Break. It resets the chain gauge, and he can use it pretty much whenever he feels like it. It's less deadly and more just irritating, although it can be problematic in the Paradox Scope fights.
Raspatil's Aleph Zero, which is a fairly typical nuke attack that can tear you up if you don't have a defensive paradigm to swap to.
Adrammelech's Firestream in Final Fantasy Tactics Advance. In a battlefield which is much longer in one direction than the other, having a very powerful attack that hits a straight, unbounded line in one direction is a bit too much.
Sheol from Final Fantasy Tactics A2's Illua. This slows down the player while speeding up Illua and giving her Regen. By the time you get your turn again, she's taken several turns and probably recovered most of her health.
From the same game, the Gold Hourglass spell used by almost every enemy in the Bonus Dungeon, Brightmoon Tor. Does damage to your whole party and casts Slow on them. The enemies will each get roughly half-a-dozen turns before you get to go. Oh, and bear in mind the enemies in this dungeon ALWAYS get to go first, so you can start the battle then go jogging for half-an-hour or so until your turn comes up again.
Final Fantasy IV: The After Years loves making 1-2 people run around by themselves with ridiculously strong monsters. There are several ways to die near the beginning when Kain is by himself on Mt. Ordeals. An Ambush involving a snake-type monster and 2 ghouls results in Kain getting paralyzed and slowly beaten to death by the zombies. As soon as Paralyze wears off, the stupid snake does it again before Kain gets another turn. Also, just after that, The Hooded Man loses Ceodore on a cliff face, and gets ambushed by Medusas, or Rock Lizards and gets petrified before he can even do anything. Honestly, you'd think the game developers would have more sense than to put monsters with such deadly status attacks in a situation when you only have 1-2 party members....
In Dissidia: Final Fantasy, Chaos has several attacks like this. First is Divine Punishment, in which he summons exploding flame pillars around your character, stabs you with a flying sword, and then deals HP damage with an enormous explosion. People new to this fight will die to this move a lot before finding out the trick.note When he starts it, don't move. If you stay in one place, you'll dodge the flame pillars. Then dodge to the side just as the flames end, then jump away from where the explosion is going to land. In phase 2 and on, he has Demonsdance: a long string of combo hits that hit you for HP damage several times within the combo (and if he's used his summon to freeze his Brave value so it doesn't go down...) and can kill you in seconds.note However, each section of the combo can be dodged. There's a rhythm to it. Finally, his last phase gives him Scarlet Rain; a merciless shower of meteors for insane damage.note You have to get off the ground as fast as you can, and then block the otherwise undodgeable meteors. The last one has to be dodged, not blocked, if you want to avoid damage. They can all be dealt with, but they are easily Chaos's most unfair tricks.
Legendary That One Boss Wiegraf's signature move is Hallowed Bolt, a long-rage Holy-elemental attack that takes effect instantly. Because the battlefield in which you fight Wiegraf - alone, mind you - is so small, he can hit you with it on the first turn. A second hit from Hallowed Bolt will kill you, no matter what class Ramza is or what equipment he has. Literally the only way to survive Hallowed Bolt is to heal after every hit (Auto-Potion and Lifefont are both godsends for this), and then boost your speed stat up high enough that you can kill Wiegraf before he uses it. Agrias and Cid both have Hallowed Bolt, but they never get to use it to completely own a duel in the way Wiegraf does.
Shirahadori, a reaction ability as opposed to an attack, can get super annoying when you're attacking the Marquis Elmdore, as he has a high chance of automatically blocking any of your physical strikes. This is another move you can use for yourself with the samurai class.
And, last but not least, Celia and Lettie's Suffocate, an instant-hit, instant-kill attack. Bad enough on its own, but the context makes it even worse; on the Riovannes Roof, you fight Celia and Lettie with Rapha in your party as a mandatory guest. Rapha's death causes an instant game over, but as Rapha's AI has essentially given up on life (perhaps for understandable reasons)she'll happily charge right in to Suffocate. Over. And. Over. Again. ARGH!
Quite possibly the most notorious attack in the game is without a doubt, Asmodeus's Sidewinder ability. Not only does it deal massive damage (to everyone in the party no less) but it can also inflict nearly every single status move in the game, bar petrify (which he can already do, no less). And the worst part is that its spammable. You better pray to the high heavens your healer doesn't get silenced.
Beelzebub's "Fall of angels" if not stopped, can dish out massive damage that almost always KO's your party. Thankfully it takes a few turns to charge up, giving you a small window of opportunity to stop it, which will result in the hilariously named "Beelzeteor' which damages him significantly. However his defences get a serious buff during that time, so you need to hit him with as much power as you can throw at him.
In the same boat as Beelzebub, Leviathan has an attack called Tsunami that takes quite a few turns to charge up. If you don't stop him before he finishes charging it up, you're going to at the receiving end of a an attack that is more than capable of wiping out your entire party, should you not have anything to resist water. Likewise, Leviathans defences are buffed during this period, making it rather hard to bust through.
The final boss has an ability appropriately named "Big Bang" which not only dishes out a veritable ass-ton of damage, but is also spammable. This can be incredibly infuriating to lose to, given how far you have to travel through the final dungeon to get to him.