There are many examples in the series. Special mention goes to Tigrex, Rajang (especially the Golden Rajang), Diablos and the Hitbox Dissonance-driven Plesioth.
In Tri, every boss can be hard if you don't have the right equipment. However, there's the Deviljho, a monster who has incredible amounts of health, deals high damage, and will repeatedly force a restart (regardless of what armor/weapons you have). Even with sleep bombing, traps, and a heavy supply of afflicted meats, this monster is nearly unstoppable. Deviljho is so bad that if you encounter it on any hunt where it's not your primary objective, the game flat-out asks if you intend to try and go for the free hunt bonus. If you say yes, it adds nearly an hour to the mission's time limit.
Tri Ultimate gives Brachydios. Its attacks are incredibly hard to dodge, and if you do get hit, you get covered in slimy mold which promptly explodes. Never mind the huge damage it already deals out. And it leaves that stuff everywhere, and combined with the huge arsenal of those certain attacks your health will sink fast. It goes From Bad to Worse when it enters rage mode. You might as well run, because its souped up attack and insane speed will decimate you if you aren't prepared. Lesson here: always be Crazy-Prepared.
White Fatalis is considered one of the toughest monsters in the entire Monster Hunter series.
Perfect World has, among others, the Nightspike Bloodguard (previously called the Mantavip Scout). The problem with it is, not only is it extremely strong, very hard to tank (he uses magic attacks, which will kill a barbarian, and arcane classes don't have that much health), but it has 2 Dragon of the Depths as pets. That's 2 more bosses, swimming around it and killing your party along with those damn water casts. Oh, and he has AoE. And so do the Dragons.
Draconis the brown dragon, from Baldur's Gate II: Throne of Bhaal, is widely considered one of the most frustrating enemies of the game despite the fact that his storyline role is essentially that of a door guard for his Evil Overlord father (who is considerably less difficult, as is every other boss in this extremely poorly balanced expansion). The problem with Draconis is that by the time you encounter him, you probably think you have dragon-slaying down to a science. Then you find yourself facing a dragon with high-level spellcasting abilities, who can buff and protect himself in ways that other dragons can't. And to top it off, he's the second part of a Sequential Boss fight that begins with his human form, meaning that any short-term buffs that you cast on your party before the battle will fade before or soon after he goes draconic on you.
Sendai is quite difficult, as she has seven statues of high level warriors, each of which results in two Drow arriving after it's defeated. You will defeat around 20 powerful enemies before even facing Sendai.
The Ascension mod, meanwhile, turns every Bhaalspawn fight (except Sendai) and the fight with Gromnir into That One Boss. Yaga-Shura's Healing Factor no longer vanishes instantaneously, but instead slowly decreases throughout the fight, and he's now accompanied by very powerful lieutenants (including a mage that can cast Time Stop,) can throw fireballs at will, and his army becomes an actual army, at least tripling in size. And that's just the first Bhaalspawn fight (not counting Illasera, who is similarly beefed up, but not quite to that extent.) The others become even worse.
Wild ARMs 2 features Kanon, who is easily That One Boss though she joins her party after you fight her three times. Her attacks, each of them, are infinitely useable, occur at random, and deliberately overpowered. The two strongest of them are her favorite ones to use, and each are capable of one-shotting the lowest defense characters of your party. The fun part? She's in the middle of the first disk. The bosses that you fight after her aren't nearly as difficult, which disqualifies her as a Wake-Up Call Boss.
Unlimited Saga has Basil Galeos, especially since you have to fight 2 other enemies before fighting him the first time. Shadow Breath can instantly lop off LP and he can use Tail Lash/Dragon Tail to hit all allies, and he can Combo his own attacks making it even more difficult and devastating.
SaGa Frontier has a few nasty ones as well. T260's final battle, the GenocideHeart, which has forms that inflict status effects and hefty (as in, 500+) damage to your entire party at the same time. Right near the start of Riki's quest you fight Tanzer, who can one-shot anyone who has less than 350 or so HP (which will be most, if not all, of your party unless you did a LOT of grinding beforehand - oh, and if you save in the room right before you fight him, you can't backtrack to grind anymore). But perhaps the most notorious is the DevilSquid, another very early boss in Asellus' quest. Hits the entire party with enough water-based damage to take them out in a single blow, and there's really no good place to grind before you hit him. Your only real shot at winning is to put one of Mesarthim's water-resisting armor items on Asellus instead or to have bought the Asura while you were still in Facinaturu (and you did buy it... right?).
The first Baten Kaitos has two fights with the three Empire generals - Giacomo, Folon, and Ayme - that are universally considered ridiculous for taking place within situations designed to screw the player over. For the first fight, you can get yourself trapped on the enemy airship with no way to level up; for the second fight, you're required to fight them twice in a row, without a break in between. Thankfully, the game has the mercy to fully heal you between the fights.
The fight with the Angel of Darkness (which comes right after Fadroh). He has a ridiculously long combo attack (8 attacks, in a game where 5 hits is a very long combo for an enemy), which he always finishes with one of two moves. The first is Binding Winds, which inflicts paralysis, a status condition so ridiculously overpowered it puts even the paralysis in Final Fantasy I to shame - in large part because it nullifies the character's defensive ability. The second is Fangs of Darkness, which causes him to be healed by the amount of damage he just did in that combo. Not in that attack, in that combo. And after you get him down to around half health, he Turns Red, and uses this combo twice per turn. If he decides to use Fangs of Darkness on a paralyzed character, well, fuck.
The boss of Zosma Tower, Ungyo and Agyo. Two giant dog-golems that pull the same trick Fadroh pulls; at first they seem easy, but then they buff themselves to ungodly levels. One buffs attack, while the other buffs defense. They're not as hard as Fadroh, mostly due to being easier to counter (fire and water), but they both have a mountain of hit points and are murder for an unprepared player. Just to top it off, Agyo also has A-Up Pentagram, which deals ridiculously high damage to a single character, and they both can inflict their element's status effect with their finishers (Pillar of Flames - Flames, Pillar of Ice - Frozen).
One-Winged Angel Geldoblame. You heard the mention of paralysis earlier? This monstrosity uses it too. However, he doesn't drain health, but rather uses it in conjunction with Forfeit Your Life. Forfeit Your Life seldom hits if you can defend against it...except paralysis removes your ability to defend. Oh, and he heals himself every turn, just in case you don't hate this fight enough.
Malpercio is the last major boss fight in the game. He still deserves to be here. His first form isn't hard at all, but his second form is nightmarish. He can do tremendous damage and move twice per turn, which is all to be expected. But, he's also a Barrier Change Boss. Ever tried resisting and damaging all six elements? Also, as you wear him down, eventually he Turns Red and busts out Enchanted Blade, which replenishes his health based upon the damage the player takes. If you can't kill him within a couple of turns after he starts using that attack, you will not be able to win. Oh, and if you can't reduce his life from 10,000 (he has 20,000) to 0 in one turn, he uses Enchanted Blade on all 3 of your characters in a single turn. This makes him the only boss in the game that gets three turns in a row (even if only once in the battle). Unless you are loaded up with some of the Game Breaker healing items (Deluxe Sushi or Wonder Momos), you're in for some serious pain.
Baten Kaitos: Origins has the Holoholobird, a hard-hitting Flunky Boss. For starters, this boss is a huge difficulty spike above the last one. It hits hard and has a particularly nasty finisher, Wingflail, which knocks the whole party down and trashes your HP. Meanwhile, it constantly lays eggs, which hatch into chicks. The chicks not only hit hard, but can also heal the big bird for huge amounts of HP. Like the trio mentioned above, this also comes right after a disc swap that will trap you there without any way to train if you don't have another file on the first disc to reload from.
Giacomo returns to claim the That One Boss title, this time by virtue of being the second boss in the game. Giacomo hits hard and fast, tearing through Sagi and Guillo's pitiful health very quickly and frequently knocking them down. Milly joins your party for the fight, but she's under the control of the AI, which is apparently too stupid to equip weapons, which makes her only useful as a meat shield. Just to top it off, your only healing items are the rather underwhelming Low Potions, the borderline-useless Herbs, and the weak revival Fate's Cordial, while your weapons and specials are severely limited. Experienced players who know the ins and outs of the battle system can wipe the floors with him, but it's a brutal wake-up call for new players.
Many people found themselves stuck on the boss right before the Heart-to-Heart scene, the Godcraft. It has ridiculously strong stats, and is easily the most powerful enemy you'll face in the game (possibly even more than the final boss!). It can wipe out half of anyone's HP with a couple of normal physical attacks, and then KO them completely with a devastating finisher. It also has a finisher that will hit the entire party, meaning one of two things: everyone will be brought down into the red zone, or you'll be left with one or two devastated characters. Due to the move's damage calculations, if you've lost a character when it uses this, you're screwed, because it'll hit the two remaining characters for more HP than they have. The saving grace is that it's weak to Darkness...except Darkness is the rarest of the elements, with only two specials being Darkness-elemental. Hope you figured out Blackest Yang!
The Black Dragon. This guy's entire shtick is his sheer power: he's one of the heaviest hitting bosses in the entire game, and also has one of the highest HP counts in the game too. He'll frequently leave someone in critical condition if not outright kill them with a single combo, and when he uses Crimson Catharsis, he'll nuke your entire party for massive damage and may leave them in flames. This battle would be nearly impossible if you didn't have the opportunity to get a Book of Mana at this point. The battle's strategy is basically to assemble the heaviest hitting light-based combo you can manage (because that's his weakness), because otherwise you'll only be chipping at his massive health while trying to keep yourself alive.
Quaestor Verus. Final Boss, yes, but still can go here just for being completely different from any other fight in the game. For starters, you have to fight two waves of tough machina before you get to him, and losing sends you all the way back. Also, you don't get a break in between waves, so After Combat Recovery doesn't kick in, making this the one mandatory fight where you have to think beyond the enemies you're currently fighting. Not healing and reviving before finishing a wave is insanity. Then, when you get there, you find out he's a Flunky Boss. He doesn't take damage until all the flunkies are dead, and he constantly revives them. Thought you could use Frigid Queen's Festival to annihilate him? FOOL! Thanks to the way the game's targeting system works, that'll only kill the flunkies. The boss himself will be unscathed, and your specials (and your best revival and healing) will be unavailable until the MP gauge turns back on, by which point he's almost certain to have introduced your party to his sword a few times, as well as reviving his mechanical pain dispensers. Also, if anyone in your party gets knocked down, he'll stomp on them, most likely finishing them off.
There's also the Hearteater which wouldn't be too difficult if not for it's Ovulate attack. Not only does the move put a character to sleep, it also starts a countdown which kills them instantly when it hits zero. There's no way to cure the character and the countdown doesn't stop for the attack animations either, so here's hoping you brought a few Fate's Cordials!
The sequential Big Cannons from Metal Max Returns. They shoot you while you're moving towards them on the world map, so you're not likely to start the battle with full armor. You only have two party members and maybe two player-owned tanks at this point. They can hit both party members with a single attack, and are capable of doing so twice in one turn. And they have a ridiculous amount of HP.
Miguel in Chrono Cross, who comes with a full complement of white magic: devastating spells, buffs, debuffs, TurnBlack, and AntiBlack. And he's very good at comboing them for tremendous damage, as well as quickly turning the entire field white, which substantially boosts his already staggering magical power. And, once his HP gets low enough, he starts using HolyLight and MeteorShower. And the fight with him is preceded by a non-skippable, 3-4 minute Exposition Break (you can run away from the battle after his exposition, save, and rejoin, but few players will think to do that).
Garai is the first one in the game. He has very strong attacks which do heavy damage to anyone. And to top it off, he is a White element, which is bad news for Serge who has recently been placed in his nemesis's body, giving him the dark element. This is probably the first boss that will wreck your main character.
The Hi-Ho Tank isn't easy either. The main threat comes from its ElementShot ability, which hits characters with their elemental weakness. Most characters can't stand up to two shots from it without healing, and it has several other attacks that are too powerful to shrug off. Also, it comes with two flunkies, who will repair the tank once it starts taking serious damage.
Polis Police, the second boss you fight on Disc 2. If you didn't defeated the Bonus Boss and got the rewards from it before coming here, you're already screwed as hell. Polis Police has not one, but two attacks that instantkill anyone thanks to it's huge damage. Not even Serge is safe from this guy. It will take 10 or more game overs to beat it if you went unprepared to Chronopolis. And it's not even 10 minutes since you switched the CD.
Giant Gloop. Attacks that can freeze your characters, which is the same as having a dead member, huge defenses that can only be passed thru if you use a hell of alot of Red Elements and an attack that at this point on the game, you can pretty much run away if you even manage to survive it.
Magus of Chrono Trigger is very tough compared to previous bosses, with powerful magic attacks that smack your whole party and change his barriers that make him impervious to all magic damage but one element of his choosing. He uses fire, water, lightning, and shadow barriers; any magic that doesn't correspond to the barrier heals him. Crono and Frog are required for the fight, so you'll be able to hit at least two elements. The third partner is where the decision comes in; taking Lucca or Robo will let you hit a third barrier (although Laser Spin is a pretty weak attack against a boss), but this can leaves your healing weak, and you need all the healing you can get. Thankfully, he eventually stops casting barriers around himself, but then he starts charging up to use Dark Matter. And if you take Marle along, it'll drag the battle out a lot longer. Thankfully, they did give you a show of mercy; Magus isn't immune to physical attacks, and repeatedly attacking him will cause him to swap the barrier, although he'll still make you suffer for it.
Giga Gaia is a giant golem you fight on top of the Mountain of Woe. You have to destroy his two hands, and then attack his head. This is easier said than done. If you leave the hands alive, they'll frequently work together to unleash a variety of powerful attacks. If you destroy them both, he'll regenerate them within a couple of turns. Just to add to that, his head has a ton of HP and his right hand can heal it.
The Golem Twins you meet in the Ocean Palace. Earlier, you fought one in a semi-Hopeless Boss Fight (it's winnable but not necessary), but this time you have to win, and the twins will not make it easy on you. Aside from powerful normal attacks, which they switch up depending on the skills you use on them, they also possess the nasty Fixed Damage Attack Iron Orb, which will instantly cut your HP in half, no ifs, ands, or buts (which is their response to physical attacks, meaning at least some of the pain will be mitigated if you go all-magic, but if you brought Ayla, she won't be much help). It gets much easier if you can take out one of the golems, but that's a feat in itself.
Near the end, you can board the flying ship called the Black Omen. The boss there is Queen Zeal. This boss has 3 forms. Aside from the usual high-damaging attacks, one of the boss's favorite attacks is Hallation. This is a "Reduce everyone to 1 HP" attack. Your healers will spend a lot of turns keeping everyone alive and reviving dead party members. Due to That One Attack, this boss can easily be more difficult than the Final Boss.
Oh, and if you attack her hands at any point in the fight, she dualcasts Hallation and MP Buster. Have fun coming back from HP to One and total Mana Burn.
In Digimon World 3 there are actually several, depending on the player: all encounters with Bulbmon ( although one is technically part of the Final Boss battle and therefore exempt), Persiamon and Raidenmon.
Exo-Grimmon from Digimon World Dawn Dusk is a really nasty step up from Chaos-Grimmon(despite being the final boss),his previous form, his attacks are much stronger than his previous form and his attacks either do horrific damage,kill your digimon of screw them over with annoying status effects, not to mention that if you die you have to reface Chaos-Grimmon who is easy in comparison and hands out large amount of EXP when he dies)The fact that getting to him involves going through enemy headquarters filled with unskippable Random Encounter just to get through the maze-like Chaos Brain to reach this nasty piece of work,the fact that the game has a high encounter rate that is unskippable just makes this even worse.
Macha in .hackVolume 4. She has an attack which charms the entire party without fail, meaning that all you can do is watch your team beat each other up and hope they snap out of it before you get a game over.
Skeith in .hack Volume 1 is much worse. Three out of its four attacks are powerful enough to bring a full-health character down to under a third of its health, and of these, one hits the entire party and is impossible to dodge (IT is also percentage based so it won't outright kill you, but one of its other attacks, which it loves to use, will oneshot you afterwards). The fourth attack inflicts enough damage so that any other attack can kill, as well as causing every status effect in the game (which is the same attack that put Orca into a coma (which you also have, by the way). And the attack that shows up a few more times with other bosses. Fun). And its second phase is worse than the first, considering how much faster it gets. Plus the fact that it likes randomly inflicting status effects on your party, for some reason. Hope you stocked up on revives - never mind that they were Too Awesome to Use up until now. It does not help that Skeith lurks at the end of That One Level, so you're already hurting, or that you can't Level Grind to make this battle easier; even at the game's Cap, all of the above still applies. And to top it all off, he becomes Cubia after you beat him, who is ALSO on this list.
Then there's Cubia Core in .hack volume 2. It can render itself immune to all physical attacks or all magic attacks on a whim, when there's a character who has zero physical attacks forced into your party. It should also be noted that this character is a Squishy Wizard who is basically the only way to deal sufficient magical damage when Cubia Core nullifies physical attacks - "sufficient" because the bastard heals itself, repeatedly, thanks to its Repth Gohmoras that it summons. A lot. Of course, this makes them a priority target, although Cubia hardly needs it as Cubia Core has three unavoidable attacks that can easily kill said Squishy Wizard. Note that after reviving a dead character in this game, they start at 0 MP. Fun fun fun.
Tarvos in the fourth volume shows just how much the developers learned by repeating almost the exact same gimmick as Cubia Core. Granted, Tarvos doesn't heal itself, so it doesn't seem nearly as bad as Cubia Core...until it decides to use CursedDeathPlay.
The sequel to .hack, the .hack//G.U., has AIDA<Oswald>. She's the first AIDA boss to spend all her time on top of you at melee range, and her melee attacks are devastating and trying to attack her with a scythe while not stunned is foolish. On top of that, her bullet attacks slow you (to make you easier to smack around), her homing attacks tend to hover out of sight and swarm at an odd timing to make them harder to knock away, and her "laser" attack is a web that makes for micro-dodging hell. She'll probably be the first Avatar battle that you have to refight.
Corbenik the Rebirth is also a monster, thanks to the difficulty in Data Draining him.
Cubia's back, and has some new tricks in store. Albeit it's mostly not TOO bad, considering it's the Final Boss, the first two phases of the battle which are comprised of the last Avatar Battle in all the G.U. trilogy can be bothersome. Specifically, Cubia has an attack in the second portion of the Avatar battle that it only uses at low health, but can easily send you back to the very beginning of the entire fight, which is quite long to begin with. The attack is Chaos Gehenna, which causes a stream of large, explosive Gomorras to fly at Skeith. The attack can deal huge damage, and it's almost impossible to destroy or dodge all of the suicidal Mooks. The Cubia Core can once again give problems as well (if you're not overleveled, which makes it an Anticlimax Boss), since it sends an unending stream of Gomorras at the party, and it's Right Core can inflict multiple status effects, the most dangerous being Charm, which is basically a form of Confusion that cannot be cured by whacking the afflicted over the head. The main core itself can also fire many energy beams out of it's mouth, fly away and ram the platform the characters are standing on during which it cannot be harmed, and it's cutscene attack that makes energy blasts literally rain upon the party followed by a large explosion can hurt.
The Mages Tower has some tough encounters but the infamous boss that takes a disproportionate part of its mission is the Sloth Demon. When encountered it sends the player character and their squad to sleep and traps them in a realm in the dream world. The player character has to move from one place to another PORTAL style, gain powers from NPC's, rescue your squadmates, kill all the mini bosses and THEN you confront and kill the Sloth Demon in a tough fight where it changes form. Dealing with the Sloth Demon takes more time and effort than defeating the main boss of the Mage's Tower.
Notably from Orzammar is a fight against several Yellow/orange enemies, including a Templar (who is basically a toned down Revenant with higher health/damage), a Blood Mage (who is broken by sheer merit of being a blood mage), and dangerous mooks.
The more notable boss of the Dwarfs recruitment mission is the Darkspawn Broodmother. As if her grotesque appearance and horrific origin story aren't bad enough, there's the boss fight. The Broodmother has high levels of health, summons many tentacle ads that can stun the player along with Darkspawn ads. Players attacking her in combat can be grabbed and subjected to a one hit kill or an Ao E, that both involve vomit (literal Nausea Fuel).
"Witness Gaxkang!" Not to mention that the fight takes place in a tiny, cramped house where your party has no room to maneuver, and he can effortlessly wipe out your whole party with his deadly area spells.
Leliana's Song has the mage fights from the prison sequence. You have crappy gear (having lost the stuff you should have), a probably useless spec, and only 2 members to deal with an array of lethal mages and nigh unstoppable Mabari Warhounds. There is also the fight against an Amulet's guards.
The Golems of Amgarrak ALSO does this so often that it hits That One Dungeon levels, the worst example likely being a room containing four Boss-level golems with two Elite golems as backup and precious little room to maneuver. Expect to spend most of the fight flat on your back from a barrage of highly-damaging Slam, Quake, and Hurl attacks.
The Ancient Rock Wraith at the end of Act I. It has massive health, massive armor (that only goes down after it uses a special ability), this special ability dealing AOE damage to your characters, deals huge damage, has huge range on it's melee attack (in addition to it's ranged attack), and summons mooks.
The next one is the Arishok, at the end of Act II. Normally, you fight him with your full party, against him and a bunch of backups. This is a hard, but not unbeatable fight. But, if you choose the right options, you can fight him one on one. Almost regardless of your build, this is a nigh impossible feat of endurance if playing above easy.
From the Legacy DLC, we have Corypheus. The former Tevinter Magister-turned-Darkspawn Emissary hits like a bus, boxes the players in with a maze of rock spikes, and is invincible for most of the fight unless the player can both activate a series of switches spread around the arena and kill off all his minions in a short time. Why a short time, you may ask? Because you only have about 20 seconds before he hits you with a nearly unavoidable gout of flame that he'll continually sweep the field with until you take care of everything else. Did we mention that he fills the field with other hazards such as mazes and elemental traps to slow you? Or that the only safe areas on the field are extremely small spaces behind corners next to each of the switches? Or that your AI allies aren't smart enough to run away from the giant flamethrower on their own, leaving you to constantly order them out of danger (neglecting your own character in the process) or watch them all die? Or that his minions are unaffected by all of this and will try to flush you out to die? Because that's what he does.
Lampshaded by your party members:
Varric: What, he has fire now?
Merrill: He absorbed it from the statue.
Varric: Sweet Mother of Pearl!
Hawke: Watch out for the ice!
Fenris: And the rocks! Don't get too close!
Varric: Okay, if he pulls a dragon out of his ass, I'm leaving.
Dhoulmagus from Dragon Quest VIII. This boss fight consists of two consecutive confrontations with the Monster Clown, each being very difficult due to the boss' vast amount of powerful attacks, some of which have effects that haven't even been introduced in the game at that point, and ability to attack TWICE per turn. The majority of the bosses after Dhoulmagus are also brutally unfair, with the stupid icewave move that'll obliterate your carefully built up status buffs and tension, AND multiple actions per turn. Empyrea is ungodly. Oh, and apparently she was just testing you.
The two dragons guarding the entrance to the Final Boss encounter in Neverwinter Nights. One dragon is a massive pain in the ass to fight. Two are just ridiculous.
And, arguably, the room full of elite Old One guards right after them. Particularly considering you've barely any room to maneuver and can't use the Stone of Recall in that area.]
The Fire Elemental from Dragon Quest VII also deserves a mention here. When you battle him you are forced to use Maribel who at that time is far behind the rest of your and is likely to die in one hit. There is a piece of armor that can protect her from his attacks, but it's sold in a shop that is unavailable at the time of the fight. So unless you have the foresight to buy that armor ahead of time you're pretty much out of luck.
Neverwinter Nights 2 has the three Shadow Reavers shortly before the final boss. They ambush you on a narrow bridge, blocking your escape on both sides and severely limiting your mobility. If your melee warriors are on the wrong side of your spellcasters, you're SOL. They are immune to most types of attack, and will continually regenerate until one of the characters speaks the words of power to make them vulnerable (this must be done for each Reaver). Only two characters can do this, and one of them is the party's only cleric, so that character is out of commission for several rounds while speaking the words, and can't cast the all-important Mass Heal. If the character is damaged while speaking the words and fails their Concentration check, they have to start over. Meanwhile, the Reavers emit a shock wave every time they regenerate, knocking your party down and stunning them for a round. This fight is virtually impossible to win unless you specifically prepare your party's spells and items for it in advance, and even then it will often take several tries.
Only available to evil players is the Final Boss fight against all your former companions, a fight that is so difficult it almost feels like the game itself is punishing your for your Face-Heel Turn. The best case scenario has you and one former companion, if he survived and if you had high influence, against the other six, who have two tanks, a healer, two spellcasters, and a bard. The worst case scenario has you fighting those six plus an extra three by yourself. Even the best case scenario is notoriously difficult, since the AI suddenly becomes a lot smarter and keeps the healer and spellcasters away from you, forcing you to waste time whaling on the tanks while being barraged by ninth-level spells. Who's Laughing Now? indeed...the worst-case scenario, meanwhile, is near impossible to win without deliberately sabotaging your former allies beforehand, and even then it frustrates some players enough that they resort to God Mode.
The Queen Bee in E.V.O.: Search for Eden, for being a flying tank, essentially, with an uncharacteristically erratic flight pattern. Also, the Mother Yeti, for doing heaps of damage and causing knockback.
The Yeti in the next stage is a real bastard, too.
Legend of Legaia has the Berserker. A monster so powerful that it will give you nightmares—a hideous giant green mantis driven to the brink of insanity and over by the corrupting power of the Mist, it lurchs about with ridiculously powerful strikes and gives you the previously unseen status effect, Rot, which blanks out random attack commands.
The battles against Gaza later in the game were also insanely hard. The second fight was especially hard if he abused his attack-all move, Neo Star Slash, which did over 1,000 HP each time. Underleveled players will likely see Fragile Speedster Noa going down in one hit every time from this move.
The Renegades in Paladins Quest, a pair of nasty sword-wielding bosses whose attacks can quickly shave off large chunks of your party's HP.
Verminator in Secret of Evermore, whose devastating spells can wreak havoc on an unprepared party. Because he's up on a big stack of boxes, your melee attacks can't reach him. By the way, your "party" is two characters, one of which is your dog who only has a close-range melee attack and is therefore worthless. The only attacks that can hit him are spells, and charged spear attacks, so we hope you've grinded some offensive magic or raised up a spear a level or two.
Salabog is another one. Most of the time its spent out of range; you can only hit it while it dives in, and that's a hit on your part if you don't do it right. You also probably don't have enough ingredients to pound it away with alchemy. You can use your newly acquired spear as well. But the kicker is that Salabog has 2000 HP, and is the second actual boss. Thraxx, the first boss, has 600 HP.
To make matters worse, you can level up the spear to enable the boy to throw it. It doesn't take too long, but you do a pitiful amount of damage.
Rimsala is also the next one up. It has a short window of vulernability. There's also four statues near where Rimsala stays at during this time and they spam Flash. Despite Flash being a weaker spell at this point in the game, it's overpowered. You can outrun Flash though.
Dugog from Puzzle Quest: Challenge Of The Warlords. He's the first storyline boss you face, has a weapon that randomly does + 12 extra damage, gets an extra turn every time he gains gold, and sports the Double Roar spell which is capable of killing you instantly. And at this point in the game, you probably won't have the stats or equipment to beat Dugog on anything other than luck or serious Level Grinding.
Spiky Tiger in Secret of Mana, particularly notorious because he's the third boss in the game. (Of course, part of the reason he's so tough is because magic is overpowered, and he's the strongest boss in the game before magic is available to the player.) He jumps around the arena, with each jump knocking off huge amounts of HP and being extremely difficult to avoid. Occasionally, he'll roll into a ball and ricochet around the room or chew on one of your party members for a while, both of which do unreasonable amounts of damage. Every now and then, when he feels like adding in an extra bit of suffering, he'll jump onto a ledge in the room and attack with fire spells, which paralyze and damage whoever they hit. Just to add to it, if you haven't leveled up the bow or boomerang any, you won't be able to damage him when he's on the ledges.
Biting Lizard, which is right after Spiky Tiger, is a deceptively long boss. Most guides will tell you it has about 300HP. Except it heals itself three times to almost full HP. And it has a habit of chewing on one of your characters for a decent amount of damage for a while.
The Fire Gygas right after Spikey Tiger is this too for a player who hasn't learned to magic spam. All gygases count if you don't use magic. They very frequently change into an unhittable vapor, often magic spamming the player instead.
Boreal Face, the souped up Palette Swap of Tropicallo, has an enormously high magic defense. Up until this point the player was probably relying on magic for quick boss fights. Boreal Face actually will still have more than half its HP left by the time you unloaded Popi's MP (included using Faerie Walnuts).
Magic is so overpowered in Secret of Mana that one of the hardest bosses in the game was the vampire, purely because the mechanics of the fight made spamming his magical weakness difficult. This guy can kill a full HP party member with a single spell, sometimes 2 members if you are a bit underleveled.
The Snap Dragon has the ability to eat players, which not only almost certainly kills them, but restores its health in the process. To make matters worse, if you don't walk out the front door of the Grand Palace and save, you will end up doing it all over again if you lose.
Duran/Angela: The Darkshine Knight. Being a super-powered version of Duran's class, he also has 2 of Duran's strongest techs: Vacuum Sword and Eruption Sword. Both can peg your whole party for 300-600 HP, which will kill you if you're not at or near full HP. Actually beating him basically comes down to him not using his Techs twice in a row, because if he does, you die, no ifs ands or buts.
Hawk/Lise: Bigieu. She transforms into a cat-like creature right when the fight starts, giving her some nasty physical attacks including Rose Highclaw; it's not really a One-Hit Kill, but it does so much damage so quickly that it might as well be. Add that to the fact that she can heal herself and drain HP with Moon Saber, and you've got yourself That One Boss.
Kevin/Carlie: Fallen Cleric Heath. Not as powerful as the other two, per se, but he's notable for simply being so tough to kill. He has no elemental weakness, is immune or resistant to almost all magic, and he can use several summons from both Carlie's and Lise's movesets, including Marduk (which causes silence in addition to doing multi-target damage). It also seems that some developer added an extra 0 to his HP, as his fight seems to take longer than any other fight in the game, including the final bosses.
The Kevin/Carlie path also gets to fight Deathjester, his Monster Clowndragon. At the start of the fight, he splits off two invincible copies, forcing you to guess which one can actually be hurt. Even when you do find the one you can damage, you have to hope that the game's auto-target system for physical attacks figures out which one you're going fo. While you do that, he's casting all sorts of nasty spells to hit you with debilitating status effects like Snowman and Mute, which at the worst will completely incapacitate one of your characters, and he's always casting. Oh, and did we forget to mention his instant-death spell? The one he likes to use three times in a row?
Moon God-Beast Dolan. Aside from being one of the stronger God-Beasts overall, when his HP gets low, he will use this attack called Spiral Moon that in addition to being his strongest attack, temporarilly LOWERS your max HP. Darkness God-Beast Zable Fahr, being the last one you fight, will also be quite the challenge, even though you get a class upgrade, which you will be very grateful you got, before you fight it. First you fight these two heads that hit you with stat lower and status effet moves (special and magic attacks in the World of Mana series can't be dodged, so you can't do much about them), and then the real monster head appears and revives them. If you kill the two weaker heads, the main one will revive them, so only attack the main one, which the death of will kill the other two. The main head will attack with powerful dark elemental attacks, very nasty when coupled with the stat lower attacks the other two heads, and has the spell that kills a character instantly if his/her level is lower then Zable Fahr's.
Legend of Mana is known for being Easier Than Easy, but it still has a couple bosses that can be Hell if you go up against them underleveled or undergeared.
Tropicallo. He's a big plant hanging from the ceiling with two heads (a fighting head and a magic head) that you have to knock off his body and destroy. Every head killed does a set amount of damage to his health - he's otherwise invulnerable. At higher levels, he becomes a Marathon Boss. But the thing that puts him well into That One Boss is the magic head. It releases an area-of-effect attack that one shots you. And the area you're fighting Tropicallo in doesn't have much room to maneuver. So if the fighting head knocks you into the magic head's AOE, or you accidentally knock the Magic Head into the wrong spot... start again from the beginning.
Tropicallo has a younger brother named Labanne. Labanne's magic head does somewhat less damage (although still enough to one-shot you at high levels) and he's fought in a more open area, but he can still be a pain.
Boreal Hound has particularly hard to dodge special moves, and he uses special moves so regularly that you'll be lucky to get your own special moves off on him.
Vadise and Sierra. Sierra is very fast and stabs you in the back if you try to fight Vadise first. Vadise throws nukes at you, so that every time you get Sierra pinned down with a combination attack you have to run away to avoid it and let her free.
Star Ocean: The Second Story has Vesper and Decus in Fienal/Phynal. First, they're the first boss fight that the bosses have voices in, and they taunt you to start: "You insignificant bugs!" and "I WILL BURN YOU TO THE BONE!" They then proceed to do just that, with Decus throwing out a fire-based physical attack that is easily capable of one-shotting the whole party and Vesper backing him up with a beam move which hits multiple times and causes status ailments. Add to this the fact that Level Grinding takes forever in the area since the random fights don't give a whole lot of experience, and you've got a recipe for good old fashioned controller throwing.
There's the Grigori bosses in Star Ocean The Last Hope who are all pretty much That One Boss because by the time you encounter them, they'll usually be tons more difficult than anything else you've faced in the area they appear and they have certain points on their bodies which must be hit if you are to do anything resembling decent damage. It doesn't help with the fact that said weak spots are pretty much stupidly difficult to unveil, let alone hit.
The Phantom Soldiers on your second visit to the first planet are an awful test of endurance. You fight eight waves in a row with no break, and while it's pretty hard to do any solid damage to them, they can certainly hurt you.
It isn't the damage that's the problem, it's the fact that they can spam a range attack that can stun you and interrupt your casters. The biggest problem, however, is the Leaders, who have an aura buff that makes the soldiers hard to kill. The trick is to Dispel it.
In Alundra, the Soul Leach from Giles' Nightmare easily counts as this, considering it already has the rare honor of combining Wake-Up Call Boss and Early Bird Boss the first time you fight it in Kline's Nightmare before it escapes. In Kline's nightmare, you had to protect Kline from being swallowed by the soul leach since any damage done to him would hurt you too because you are inside of Kline's subconscious dream. In Giles' nightmare, this is taken Up to Eleven since it's now much more powerful and you have to protect Giles at all cost since if Giles is swallowed by the Soul Leach even once, you instantly die no matter what. It's said that this fight is almost impossible without a Wonder Essence (which is an auto revive item like the fairies in The Legend Of Zelda) due to it's difficulty. The best part about this whole ordeal is that the Soul Leach is the boss of Those Two Levels. At least in Kline's nightmare, the save point is close to the boss door in case something goes wrong. In Giles' nightmare however, you don't have that luxury as the save point is extremely far from the boss room, which means that if you mess up the boss fight, you have to go through most of the dungeon again just to reach That One Boss.
The Watcher In The Water comes pretty close to combining That One Boss with Wake-Up Call Boss and Early Bird Boss also. It's an earlier boss and doesn't do this to the level of the aforementioned Soul Leach does later in the game, but it still counts mainly because it has a lot of health for that point in the game, a good attack radius, and your offense and defense are both extremely limited which makes this fight much tougher than it should be.
In the first Suikoden game, the Zombie Dragon will be the bane of an underleveled team since it can hit the entire team For Massive Damage, and you don't have a lot magic at this point which means you have to perfectly balance physical attacking and healing with your items to have the smallest chance of victory. What might help is building up your two new teammates' weapons at the Blacksmith so they hit harder, as well as taking the Clone Rune, which you likely picked up earlier, and attaching it to Viktor.
Also during the raid on Kwanda Rosman's fortress, you have to fight The Dragonwhich is actually a real dragon and have to deal with a fixed team, and also the fact that the dragon has incredibly high health and evasion which will make most of your physical attacks completely useless which will make things a lot tougher considering you don't have access to really powerful magic at that point in the game.
One of the duels,between Pahn and Teo, full stop. Not only do you have to make sure that your fighter is at a really high level (i.e., must be in your party since recruitment basically), but you also have to read the enemy's next attack (as what they say is a giveaway), or defend constantly and hope that he uses his special attack. The important thing about this battle is the fact that if you lose, that character is Killed Off for Real and that prevents you from getting the good ending, so you MUST WIN.
Neclord definitely counts for this considering that he can hit your entire party For Massive Damageand hits your entire party with multiple status effects at the time. He also has high health, attack, and physical evasion which means you better have some strong magic and healing or else Neclord will wipe the floor with your team.
The fight against Sonya Schulen in the Shasarazade Fortress counts, because you face her not long after fighting an incredibly tough other boss and you can't save in between the fights.
The battle against Luca Blight from Suikoden II is generally considered to be the toughest fight in the game for a variety of reasons, despite the fact that you attack him with THREE squads. And guess what? It's in-universe too!
It gets worse, there's a duel with him at the end. Even though he's at half health and you're at full, if you screw up even a few times, game's over. You'll have to redo that entire battle again. And since he's Made of Iron, he takes way more hits than you'll ever do.
In NetHack, Master Kaen has the highest base damage in the game, the Eyes of the Overworld which give him immunity from wands of death, and he ignores Elbereth, which can be used to hold off most other enemies. Making it all the worse is that these strengths are especially dangerous to Monks, who are the only ones who have to deal with him anyway.
Demogorgon has everything. He moves fast, has a ridiculous number of hit points (he's nearly twice the level of the ostensible final boss...), casts every spell in the game with the same massively inflated level, has 95% magic resistance, pursues you between levels, teleports away to rapidly heal if you manage to injure him... oh, and he has an attack that puts you on a countdown to sudden death, and every subsequent hit cuts the countdown by two thirds! Most damnably, whether you will meet him is entirely random: Demogorgon appears whenever Demogorgon wishes to (he has a 1/200 chance of hijacking any summon spell cast in Hell) and there is very little a player can do to avoid or (for masochists) encourage him. (If you are a masochist: there's a faq for that.)
The Wizard of Yendor himself is mind-numbingly annoying - and dangerous as well. His abilities include casting powerful spells (some of them capable of being instantly lethal) as well as stealing certain important MacGuffins and creating clones of himself. And as if that wasn't enough, he won't stay dead - even if the player kills him or escapes the level, he will periodically cast nasty spells on the player or even return to fight in person again until the player reaches the Astral plane.
The most notable one is Bundt, a cake that comes to life and attacks you for no reason. It straddles the line between either ridiculously easy or extraordinarily hard to kill, with very little space in between, depending on your characters' level (and more specifically, their defensive stat). Unlike all other bosses, Bundt has no HP - you have to knock out all of its 5 candles and then hit with a single attack. One attack from you knocks out one candle regardless of attack power, and one attack from Bundt restores one candle. You have three characters, and the cake has two parts, though only one of them lights a candle each turn. If you can manage having everyone in your party attack each round, the fight will be over in 4 rounds or less (well, the first part of the fight, but after that the more conventional second part is a pushover). Of course, that means you have to be able to tank 4 consecutive rounds of pretty hefty magic without healing once, so...
The Axem Rangers are plenty tough, considering there are five of them, and each one has a different variety of attacks - Red and Yellow hand out massive physical damage, Black counterattacks everything, Pink heals, and Green blasts you with powerful magic spells note Attacking Green first works much better than attacking Pink first, he's got so little defense he'll go down in 3-4 attacks, and the blockable physical attacks of Red/Black/Yellow are much easier to contend with than Green's spells. Even on the 20% chance that Pink heals him, because of his pitiful defense that's one extra turn. And even after beating all of them, they "combine" with their Zord/warship thing for one more go, using the insanely powerful Breaker Beam attack, which does about 70-90% of your character's maximum health.
Yaridovich completely counts for this, as right after you get the star from the Sunken Ship and return to Seaside Town, he takes it and you have to beat him to get it back. So how tough is he? His health and attack are both extremely high for that point in the game, he has powerful magic attacks that like Water Blast which hit your entire partyFor Massive Damage, and he can also put negative statuses on your characters for good measure. If that's not enough, he can also duplicate and use his moves twice in a row, and only the real Yaridovich takes actual damage until he decides to heal himself. When the duplicate is eventually destroyed, he can bring it back and make the fun start all over again. This is a sign that the game isn't messing around anymore, and that constantly attacking over and over again isn't going to win every battle.
Bowyer, the second boss, mainly because he can shut off one of your attack, magic, or item commands for several turns. While you do get a new party member for this fight, he's capable of shutting of your attack ability forcing you drain your limited magic points to zero, while he continues to attack you with powerful magic that hits your entire party and keeping your attack ability locked, leaving you helpless. Then, when you're low in health and magic points and need to use your items to recover, he'll switch on your attack ability and seal your item ability, which prevents you from healing, and forces you to continue fighting him while you're exhausted.
Don't forget that he can alternatively seal your special ability, causing the fight to become a long battle of attrition as your magic is sealed, limiting you to normal attacks while he can still rain destruction upon you.
The Tarantula in Lufia II: Rise of the Sinistrals is a pretty big kick in the nuts to first-time players, boasting high HP (relative to your damage output), the ability to summon smaller annoying enemies to aide him, an attack that knocks off a lot of damage from all your party members while having a good chance of poisoning each member, and a normal attack that also happens to have a chance of causing full paralysis to the target. Oh, and it heals, too. Fortunately, it's weak to Fire, and the previous dungeon coughs up a good Fire weapon. But unless you think to go back there after the boss is gone...
Amon in Lufia: the Legend Returns is incredibly difficult due to the battle mechanics of the game. You have nine characters at a time in battle, and you can only act with three of them. Amon has a confusion attack that hits all nine of your characters, and confused characters can always attack. If you're unlucky, you can end up with eight confused characters attacking (and slaughtering) your lone non-confused character. There is an equippable item that will protect from confusion, but there are only three of them in the game...
Guard Daos from Lufia: the Legend Returns is no slouch either. He has the very same confusion attack, as well as other attacks that hit your party for major damage and cause all sorts of status effects, a move that majorly increases his already-high defense, and to top it all off, he has a ton of HP. Oh, and once you finally beat him, you have to fight another boss immediately afterwards, and if you lose to that boss, have fun beating Guard Daos all over again. Said boss is a Breather Boss, though, so it's not all bad.
The Monster Rancher series doesn't really have bosses per se (Well, Monster Rancher EVO did, but that's... well...), but it does have tons of computer-defined opponents—some of whom could easily be That One Boss, despite actually being "That One Monster." There are too many throughout the series to list all of them, but there are a couple patterns:
In the first game and if you lack speed. Golems, There was one in every grade (E was avoidable, every other grade was not). They had enough power to KO your monster in one hit possibly killing it afterwards, and worst of all many of the times you have to beat the said golem to win the tournament.
Monster Rancher 2 had a species of monster known as a Gaboo. These had extremely high life and ridiculous attack. As you may have expected, they're absurdly hard to defeat, and some of their attacks can actually KO your monster in one hit.
The PC's Vampire: The Masquerade—Redemption had Mercurio, a rogue student of necromancy who popped up quite early in the game and proceeded to walk all over the small party with persistent area-effect attacks to which he himself was immune. Had to be nerfed by a patch as too many people were complaining about how tough he was.
The first is Ming Xiao, who starts off with a Nightmare Fuel-riffic transformation into her final form, a giant tentacular blob of goo that can spawn copies of itself, on which superpowered attacks are next to useless; you're basically screwed if you don't have a high Firearms skill and the flamethrower, and even then, if it wasn't for the game letting you save during a fight, an unfortunately-timed spawning can destroy you.
The second is the Sheriff, who also transforms into the Chiropteran Behemoth; again, you need some crazy firearm skills and the sniper rifle to take him out, and it's a long, long slog. There are two little things that can even out the fight, though: you can activate various high powered lights on the roof top which blind him, bring him to the ground and allow him to be wailed on with melee weapons & your fists for a bit, and b) he intermittently flies down to the street below and returns with a mook who was walking past. Still, should you decide to take on the Sheriff, prepare for the fight of your un-life.
Also from Bloodlines, Bishop Vick. He's super fast and has a shotgun with unlimited ammo. If you decide to turtle, you'll either get ganked by his army of zombies, or Vick will just superspeed next to you and kill you in half a second. He's also a vampire, which means that he's extremely resistant to bullets himself. To make things fair, you can hit him while he reloads, but even if he doesn't complete the animation he receives a full six shells (although it seems like more) to destroy you with. Unless your character is completely combat oriented (which the game actively discourages), your only hope is to pray that the AI bugs and Vick gets caught in a loop. Unlike Ming Xiao, he's optional, but beating him is required to complete a long sidequest chain and get an extremely helpful item.
Lenus from The Legend of Dragoon. Casts ridiculously powerful spells that hit everyone, uses a physical attack... that hits everyone, and is so fast she'll likely get three or four turns in a row before your party gets to act. Better hope you've done enough grinding to get Final Burst!
The Grand Jewel can also count. It can mess with your character's levels, changing them by 5 at a time, and it loves to lower your level multiple times in a row before actually increasing them. And it's even worse if you've gotten into the habit of getting as much of your transformation gauge filled as possible before using the Special command (all characters take on their Dragoon forms); doing that will make him use the Dragon Block Staff, which makes your Dragoon forms pathetically weak.
Jiango can be a hassle as well. While you can put him to sleep for a while with the Sachet provided to you in the same room, he still hits quite hard and will seriously test you after he wakes up. His most powerful attack hits your bulkier party members for close to 70 damage, while squishier characters (and Lavitz, since Jiango is Earth and Lavitz is Wind) can easily take over 100 damage each time it hits; said attack also hits your entire party, and Jiango has a tendency to spam it.
The Arthrosaurus sequence. You encounter the beast as you approach Numara and have to face it to progress. It has just over 14,000 HP, and only has two attacks: a physical strike that deals around 200 per character, and a fire based attack that can do around 2000 damage to every character in a single line of your formation. A somewhat lengthy, but not too terribly difficult battle by itself...but then 4 more appear off the coast of Numara, and start heading for the city. You have to defeat all four of them before they reach the coast, and they move at a fairly brisk pace. If just one of them reaches the city, it's an instant game over. And while you're fighting one of them? The other three are still moving.... Thankfully, Sleep works every time on them, and can freeze them on the world map for around a minute or three. The fight is meant to be a hit-and-run affair, where you wear away at one after another's health.
Minamimoto the first time around in The World Ends with You: a boss so difficult that nearly every guide suggests just setting the freaking game on easy mode.
There's a trick to Minamimoto, but it's a hell of a Guide Dang It: his chain teleporting is triggered when he's touched with the stylus - as in, you the player touch him on the screen. Notably, he's the only the enemy that directly reacts to being touched like this. If you have pins that don't necessitate actually touching him, he's much easier for Neku to pin down.
Uzuki and Kariya, at least if you try and fight them on Hard or above. Uzuki by herself is a nightmare, even when she's not teamed up with Kariya. She's got multiple Bullet Hell esque energy shot patterns, but the real problem with the fight is how she switches screens with her shadow self. When she does it, it has the effect of her Flash Stepping and breaking your comboes, even if she goes exactly where her shadow was on the other screen. How often does she do this? Let's just say that, on Hard, she makes Minamimoto look "zetta slow". It's really hard to pass that light puck when she doesn't allow Beat to land more than 2 hits of his (5-6 hit) combo.
Kitaniji and SHIKI. Shiki gets a massive power boost out of nowhere since she was in your party and Kitaniji can FREEZE TIME to try and hit you, and that's just on normal!! On hard Kitaniji gains 2 Bullet Hell-esque energy blast attacks, and loves comboing them with his time stop move for maximum pain...
Mikhail Rasputin, the boss of the second act of X-Men Legends 2: The Rise of Apocalypse is probably the hardest boss in the game. In the first stage of the fight, Mikhail creates many duplicates of himself which must all be defeated. Then he tosses up a forcefield that must be brought down by beating up various minions until they turn into control panels. And finally, he decides to just bring on the pain while summoning near endless goons to challenge you.
In Shadow Hearts, shortly after the Time Skip, Alice has to fight Arcane Olga in a Duel Boss fight. Alice is the game's White Mage. The fight is on a timer because of her Sanity Points (the lowest in the game), and taking a turn to restore them could get you killed. And Olga can poison you. The fight boils down to spamming Alice's one attack spell and hoping to get it over with before she goes Berserk.
Also, Joachim's teacher in Covenant when you first meet him. What makes this battle so hard? Well, he'll be using Grand Slam all the goddamn time, which wouldn't be so bad if it wouldn't randomly kill you instantly. And you only have Joachim for the fight.
Even Kingdom of Loathing has a member or two of this grand pantheon. The first, Baron von Ratsworth, is optional, but if you decide to fight him, he scales to your level, which is frustrating since level-grinding will actually just make him stronger. Defeating him on your character's first run through the game is incredibly hard. On subsequent runs or if you level up and get to access the Cola Wars Battlefield, it actually gets quite easy: get enough combat initiative to get the jump on him, then toss a Cola Wars Battlefield grenade at him. If need be, mop up with a strong enough guaranteed-hit skill.
The worse example, however, is The Bonedragon, the boss of the Level 7 quest. Apart from the Naughty Sorceress, it is the only monster capable of blocking skills and item use. Considering that it takes a rather substantial boost to one's stats to stand toe-to-toe against it compared to rest of the quest itself, it can prove to be very very frustrating. Unlike Baron von Ratsworth, however, one can just level-grind to take it on, but it can be a pretty severe bottleneck.
And speaking of the Naughty Sorceress, she herself was easily That One Boss back in the day. Like Baron von Ratsworth, she scaled to your stats, meaning she was tough no matter what, and like mentioned above, she could block skill and item use, PLUS she dispels all your buffs right at the start of the fight, constantly healed herself, and shrugged off your de-leveling effects. And she was impossible to beat if you weren't equipped with a specific weapon, which has a mere 30 attack points. With the introduction of NS13 though, she's much easier, as her stats are set around 200 and no longer requires the aforementioned weapon to beat (though it DOES have to be in your inventory).
Two of them are in Hobopolis: Frosty and Zombo. Frosty takes only 1-3 damage from any source, so quite a lot of damage sources have to be collected to chip him down within the 30-round limit. Zombo scares the pants, hat and shirt off of you, so you would have to be sufficiently leveled up to fight him naked. Skipping either of these bosses will make Hodgman the Hoboverlord That One Boss instead, as Frosty will boost his already high damage resistance, and Zombo will scare your gear off your character in one round instead of his usual three.
Duriel of Diablo II, despite being only the mid-game boss, is probably among the most dangerous of them and easily the most frustrating. For some reason, the designers thought it would be great to pit the player against an enormously fast boss, with an aura that irresistably slows the player, in a bare room perhaps eight times his area. This in a game where hit-and-run is god; half the classes are explicitly designed for ranged combat only. Another relies on enemy mooks corpses to summon minions. On top of everything else, you can't escape the room to catch your breath, even though you enter the room through a big hole in the wall.
Plaguewrath in Diablo, a frustrating spitter boss. Basically he has a bunch of minions that all act the same way: they spit at nearly double, or even triple the speed of regular spitters, which means that often they'd drop a barrage of deadly spit that can drop you in seconds, before you can do anything. Add the fact that they don't have a melee attack, and unlike regular spitters, will actively run away from you if you try to get close, and you get one frustrating boss. Not to mention that the first time you'll encounter him, Plaguewrath himself takes forever to kill.
The three Barbarian Ancients are pretty much the hardest encounter in the game, arguably topping Duriel, Baal, and even Diablo himself (who at least gave you ample room to hit and run). What made the Barbarian Ancients so damned difficult was that using Town Portal to escape would heal them back to full health, meaning yes, you had to kill them all in one go.
The councilors in Act III on higher difficulty modes. They're just superuniques, but on higher difficulties they gain a lot of traits, and sometimes those traits work TOGETHER to create a new definition of pain. Can you imagine Conviction plus Might plus Cursed plus Extra Strong plus Lightning Enchanted plus Multi-Shot together?
Lister the Tormentor is a nasty one. It takes forever to kill him, while all he does is move toward you unphased and land in a nasty punch when close enough. You can't even run away because he follows you everywhere.
The Destroyer of Souls in the Chaos Sanctuary and his twin brother, Ventar the Unholy in the Woldstone Keep. Big, strong, and faster than you can ever hope to be. Their minions also share these traits, so you will end up cornered by half a dozen monstrous demons in the matter of seconds with nowhere to run, and beaten down in just a few seconds. Ventar is only made easier because of the nature of the area you fight him in. It's possible to separate his goons and kill them one by one. If you're lucky.
Nihlathak in Act V gets one of the most powerful moves in the game: Corpse Explosion. It does 70-120% of a dead monster's maximum life as damage; he also gets the ability to spawn Mooks to attack the player and double as corpse explosion fuel after they're dead. In later difficulties, 1 corpse explosion is more than enough to One-Hit KO a character.
Diablo III continues the tradition of murderous Act 2 bosses with Belial. It's a perfectly reasonable standard boss fight with mooks, like every other boss fight to that point...and then he goes One-Winged Angel and turns into the equivalent of a World of Warcraft raid boss, complete with phases where he AOE spams the entire narrow platform where you fight him. Even on Normal difficulty it's bad, especially for the squishier classes like the Wizard.
The first few bosses in Summon Night: Twin Age are a piece of cake to beat... and then you face Mardin at the end of Chapter 6. This summoner has a wide variety of attacks and appears to be Made of Iron, as his HP are far higher than any enemy you've faced up to this point. Oh, and he loves to get up close and attack your party members head-on, so if you chose secondary White Mage Ayn instead of the axe-wielding Nassau, expect her to be defeated once or twice (putting a dent in her support value).
The second round against him manages to be even worse, you fight Mardin with only both main characters and one of them is a Squishy Wizard that Mardin can destroy in about three attacks, additionally he's far stronger and his AI seems to be set to Shoot the Medic First mode and will almost always go after her.
Xenogears has several of these throughout the game. The first one that comes to mind is the second fight against the Five-Man Band that fights for Solaris. What makes it hard is the fact that you first face two of them at once. Then you have to face three of them at once and you don't get a chance to heal before it. Then you have to face Elly with all of the damage received from the previous battles.
Redrum is another pain to fight. Not only does he have Bloody Rain, a move that will damage your party and heal himself at the same time, he also has Murder, a move that kills one character and heals himself at the same time. Worst of all, he's found in the sewers of Kislev, which is That One Level due to its size.
What makes this fight so punishing is not what he can do, but that most players may have been led into a false sense of security with how easy fights out of gears were beforehand. He hits hard and has more HP than the previous two bosses (Elly and Dora) combined.
Id is a pain to fight each time you face him since he can do massive damage to any character in a short amount of time.
One of the first fights that you have in the second disc against the Sufal Mass and Sufall. You can't do elemental attacks against him or it will heal him. If he happens to kill the last Sufal he will unleash a massive attack against your party.
The Elements also are quite a pain to fight, mostly because they can heal each other, and if you use the wrong elemental attack it will heal them as well. Don't even think about attacking Domimina until you beat everyone else or she will heal herself regardless of what you to do attack her.
Hammer is another example. When his HP gets low enough he will start to glow red and will blow up, killing everyone unless you either defeat him before he blows up or runs away. Running away however will prevent you from getting a rare and awesome item.
The first fight against Deus is a pain the ass since he starts out with one attack that cuts EVERYBODY's HP in half. If you attack before a certain point he heals himself for a huge amount of HP. On top of all this, the game has a habit of crashing during this battle (apparently if it's played on anything other than a PS1 or its digital rerelease).
The last Ramsus and Miang boss fights. Ramsus has an attack that causes HP to One in every character. If everybody on the team has more than 1 HP, he will do the attack again later on in the fight. The main problem is that you have to heal yourself and fight him at the same time while keeping an eye on your fuel. Miang is worse since she will mirror the damage done to her back onto you.
The infinitely infuriating Kromar, from Lil Monster. He's got a metric buttload of HP, ridiculously high strength that makes even his weakest attacks do almost 100 damage, and copious healing gems. However, he also makes liberal use of Meteor Drop, the most powerful attack move in the game—which does something like 230 damage per hit, coming from him. If you've been Level Grinding up to that point of the game, you're likely to have about 400 HP, give or take. Yeah. He's hard.
Varesh Ossa from Guild Wars. UGH. She is even harder than the final boss. (Granted, he is rather easy but...) She also has a One-Winged Angel form too, blegh.
Nightfall has Shiro Tagachi. The amazing thing is that he was the Big Bad of Factions, and he wasn't nearly as hard there, despite the fact that he had two incredibly annoying and powerful skills in Factions that he doesn't have in Nightfall. (On the other hand, in Factions, the mission to fight him consists entirely of "Defeat Shiro." In Nightfall, you have a fairly lengthy and difficult mission to get through before Shiro.)
Coventina the Matron... or any of the other Mursaat Monk Bosses from Prophecies. It takes a specialised -team- to take them down effectively due to the efficiency of their self-healing... and can consume a LOT of time. Makes for much trouble if coupled with OTHER Mursaat bosses.
Elementalist bosses in general. All bosses and boss-like foes have an inherent double damage bonus (on top of the bonuses they get for their level), meaning some of them can pretty much wipe a party in seconds.
Then there is Dhuum, of the The Underworld, this boss is now a MANDATORY fight to complete the Underworld where before you just had to finish the quests. Those quests? You still need to do them all first before he appears and there is no second chance, if you all die that's it, you got to do it ALL AGAIN. Dhuum ranks up there with Kanaxai and Urgoz...
Clumsy Robot from EarthBound. Fighting him is very much a Luck-Based Mission; most of the time, he'll spend tripping over his own feet, but rarely he'll throw a missile at you. Said missile hits both party members for a staggering amount of HP; often more than Jeff even has at this point. The fight boils down to just smacking it over and over, and hoping Jeff and Ness can get through its sizeable HP before it hits you with the missile attack. It doesn't help that PSI is completely ineffective against it.
Ness's Nightmare from the same game is a huge pain in the ass to deal with — first, because you're forced to go at it alone (unless you're lucky enough to keep a Flying Man alive up to that point, which is hard enough in itself), and second, because it tends to constantly use Lifeup and power shields on itself before whaling on you with high-level PSI attacks. It is possible to at least grab a special pendant that nullifies the effect of its "glorious light" attack, but waiting for it to completely drain its PP so it can be rendered useless is a big hassle. (The power boost received at the end is a sweet consolation prize, though.)
Even if you're not trying to go Off the Rails, the Kraken is a tough boss. All three of his attacks hit the whole party, and while you can reflect the lightning attack with the Franklin Badge and block most of the fire attack with a Flame Pendant, chances are you'll only have one of each by the time you get to him. Also, his tornado attack can't be blocked in any way, and it does much more damage than the other two. Finally, your nonoffensive PSI won't save you, as his fourth attack dispels any buffs, debuffs, and status effects you might have cast.
The Trillionage Sprout is a doozy. He's the boss of Milky Well, the third Sanctuary, but is very powerful considering how early he's fought. For one thing, he starts with two Tough Mobile Sprouts, which are Goddamned Bats who can call for help and heal each other for large amounts. You need to kill them first or it will be basically impossible to even dent the Sprout, who has considerably high health. He can also put up a shield to block damage or hit your party with PSI Flash, which causes a bevy of nasty status ailments. The real danger of Trillionage Sprout is when he uses an attack where he "glares with its eerie eyes", causing one of your characters to become Diamondized. Diamondization is like death; if everyone gets Diamondized, it's game over. At this point, you have three characters, but only one has the attack power to deal any real damage to the Sprout. Also, Diamondization is instant, unblockable, and hard to cure at this point in the game.
Let's not forget Shrooom!. He packs a fairly high amount of HP for the time being, but that's not the issue. What is the issue is the fact that he tends to scatter his spores on your party, which potentially sets the Mushroomization status on your team. It works sort of like Confusion, but you can still input your party's commands (they just might hit each other instead). So you can get your party ready to attack with their best moves, get Mushroomized, and watch as your party rip themselves to shreds.
Carbon Dog's second form, Diamond Dog, is a doozy. First of all, he has a tremendous amount of HP, the highest in the game in fact. He also has an attack that can diamondize (basically instant death) one party member, and the 'glorious light' attack, which is basically PSI Flash Omega and WILL paralyze or kill anyone without the right equipment. Giygas help you if you missed the Sea Pendant in the Lost Underworld. Finally, if you kill Carbon Dog with a Multibottle Rocket, say goodbye to Jeff; Diamond Dog starts out with a power shield, which will reflect the attack that finished off Carbon.
The Dragon in Earthbound Zero is a real pain, even with Ninten at level 25. Sure, a PSI-Block from Ana will make things easier, but what if the Dragon manages to kill her? You're pretty much screwed because she is the only one who knows SuperHealing at a low level.
The Steel Mechorilla from MOTHER 3. Nothing gimmick-y about him— he's just very, VERY powerful, powerful enough to beat up all your characters without the slightest difficulty. And he has a ton of HP. And he powers himself up if you cast PSI Thunder more than twice, becoming even tougher. It is not unheard of for a player to load all four characters' inventories with healing items... and end up using almost every single one.
The Barrier Trio, later in the game, are also a pain. They're a group of three stone guardians who completely negate all offensive PSI, and have devastating PSI of their own. Just for the final touch, when you're about to finish them, they throw the all-powerful PK Starstorm at you.
The fight with the Masked Man at the temple of the sixth Needle. You have to fight him after going through tougher Pork Troopers and he can consecutively attack, destroy your shields, and use high-level PSI. It doesn't help that the only remotely close place to heal before going into the two-part battle is fairly easy to miss. You have to make do with whatever you've got left after struggling through the area, which is rare for this game, as bosses tend to be tough enough at full strength.
Fighting New Fassad is brutal. He utterly decimates a good portion of players on their first time through, probably because his attacks hit everybody at once, and he can barrage you with status effects: fleas (disables PSI and Thief Tools), forgetfulness (may force you to skip valuable turns), nausea (prevents you from using healing items) and uncontrollable crying (reduces the accuracy of regular attacks), among others. When you think you're making a considerable hole in his HP...Fassad ate a Luxury Banana! and he gets back about 500-600 health points. His strongest attack is a "barrage of bombs" attack that hits your entire party for around 130 HP, and pierces any shields you have set up, at a time when your party has around 200 HP. You'll be using up your PP and items to heal everyone, giving New Fassad more time to heal, debuff and generally screw with your party. To hit the nail in the coffin, New Fassad is at the end of a dungeon teeming with Demonic Spiders that use attacks that deal severe damage to the party, and when you do beat him, you are usually low on health, and out of PP and items (in a game where there's an inventory limit), meaning that the enemies can now murder you. He's sort of like the Clumsy Robot to players who are just picking up on the series, but sadly, his healing is no fakeout.
Miracle Fassad is even worse. He's even more fond of status effects, and has moves like PK Starstorm, which do obscene damage, affect everyone, and can prevent a character from attacking. He also has some 5000 HP, and can use Luxury Bananas ON TOP OF an attack, so you'll get scenes like Fassad used PK Starstorm >> Fassad ate a Luxury Banana >> Fassad restored 587 HP!
Mr. Passion is a nasty Wake-Up Call Boss. Aside from dealing a lot of damage normally, once you get him down to about 1/3 health, he Turns Red and gets a massive attack power boost. Without making the most of Duster's special moves, you're going down. Level Grinding and Thunder Bombs will only get you so far here.
The Pork Tank is bad enough on regular difficulty, with the nearly useless Salsa, the Squishy Wizard Kumatora, and the powerful, invincible but CPU-controlled Wess fighting it. It has a powerful cannon that takes off 40 HP a shot even if you decrease its offense (both characters have about 100 HP at this point), an attack that damages both Kumatora and Salsa, and an attack that makes both your characters cry. On Hard Mode, where the HP of all enemies is doubled, it becomes an unholy killing machine with 3400+ HP. Here, it's a guarantee that Kumatora will run out of PP less than halfway through the fight. It really comes down to Wess being useful with his attacks, which he usually isn't. And if both Kumatora and Salsa die, you lose. Salsa, however, can actually imitate that tank pretty darn well with his overlooked Monkey Mimic, which is actually more like Poo's "Mirror" from EarthBound. Of course, you don't really think to make Salsa shoot cannonballs from nowhereright away.
The Jealous Bass, fought in the Titiboo Attic. It comes with two flunkies, and combos with them to hit Lucas and Boney several times with each attack. If you take out the mooks, the Bass gets angrier and powers up, getting even stronger. Just to add to that, Lucas' PSI is very limited, consisting of weak healing and one offensive attack.
Red Testament from Xenosaga: Episode III is a rather interesting example. Most fights in the game are strategic, and level grinding is avoidable, but this guy blows every boss before him out of the water, as well as the Final Boss. Being preceded by a spoilerificTrick Boss fight beforehand, and the game's Crowning Moment of Heartwarming doesn't temper this, but it may lead the player to a false sense of security. By this time, every character can have Safety and Best Ally available for use, which automatically revive a character it is cast on after they die. This is important, as Red will beat the tar out of every squishy character with incredible speed, and with Break every tough character with that same speed. Victory comes from poking the enemy to death over the course of the entire fight.
Also from Episode III: the fight against ES Issachar near the beginning of the final dungeon. She's one of the fastest ES bosses, and gets a lot of turns, evades an irritating number of attacks, and almost never misses. She has vicious all-enemy attacks, too, though none that are likely to one-hit any of your ES. These factors alone would make her one of the hardest fights in a relatively easy game, but it gets worse. She's one of the rare enemies that uses the 'defend' command, once her HP starts getting low. This doesn't sound too bad until you notice that she heals 75,000 HP every time she defends. That's as much as a mid-level Anima Awakening. And sometimes she does it twice in a row. Even if you can survive her nasty attacks, the second half of the battle is essentially a Luck-Based Mission.
Commander Cherenkov's Gnosis form in Xenosaga: Episode I qualifies, also. Not only is it him (in a surprise battle, nonetheless), he also gets two pain-in-the-rear minions with an area-of-effect attack and that's not all: if one of the minions is killed, he gets a stat boost, if he is hurt while the minions are alive, there is a high chance that they will heal him double the HP an average leveled party can take out of him in one turn; if both minions are killed, Cherenkov's stats triple, meaning he can kill any party member (except Ziggy) in two hits, and there is a substantial chance he will get two turns in a row. Worth mentioning, he's the first enemy the player encounters who can and gladly will seal the ether abilities of party members, rendering healing if not impossible much, much less effective.
Orgulla from Episode II. She was a nightmare that did terrible damage, including poisoning party members, and acquired boost at a ridiculous rate, which gave her the ability to kill your entire party in a short amount of time. The only real strategy against her was attack, heal, and pray.
The Patriarch Sergius fight at the end of Episode II. Sure, his first form is pretty easy, but his second form is tons harder. He has a habit of boosting multiple times to cast an Ether attack on the same person (the damage gets higher for each successful Ether attack of the same element) including one a version where he first knocks you down and then casting another for maximum damage, but you can't boost over enemies so you just hope your characters evade or you have enough heals ready. He also can summon a machine by the name of Proto Omega to do massive damage in one attack as well, which can be combined with an attack from the Patriarch that can send your characters in the air. And this is just a few examples. If you're below level 40 then god help you, but even if you're above that, it becomes an exercise of you healing and him doing more damage at some points.
Episode I has Tiamat who quickly becomes this trope while on foot or if your A.W.G.S. aren't at peak condition. You have to use Boosts as much as possible and the "Recation to [character]'s Consciousness" is really annoying.
The Melk Crystal from Grandia III is an excellent example. Despite being at the very beginning of the dungeon, this boss has can wipe your party out if you haven't been playing around (and given the general Grandia mindset of no-grinding-required, this is quite possible). Not to mention it has two forms with different weaknesses and resistances, and switching between them tends to cancel your well thought out commands (literally at times). Beating this boss without using one of the orb summons is a feat in and of itself.
Speaking of Grandia, the first Grandia had the fight with the female Garlyle officers Saki, Nana, and Mio all at once. Since they've been played up as the Goldfish Poop Gang up to this point, and since they were pretty easy when you fought them individually, you're probably expecting an easy fight, right? Then they use a little move called Trinity Attack that hits the entire party for huge damage. Even though all three girls are used in the move, it only takes one girl to actually do it and the other two still get their turns (which might be another Trinity Attack)? Getting hit by two Trinity Attacks, one right after the other, can be very hard to come back from.
And lets top it off with Grandia II, and the Eye of Valmar. You got this bossfight twice, and they constitute the hardest and second hardest boss fight in the game. Earlier in the game, you got into a fight with four smaller eyes as a mini-boss, and they were Demonic Spiders that were capable of doing a lot of damage very quickly and took a long time to kill. The Eye of Valmar would be hard enough as it is, being a typical Valmar Body Part boss (meaning stronger than usual) and having an ability to completely immobilize one of your party members, but it comes another set of four smaller eyes!
Legend of Mana tries to avoid making baddies too difficult; either placing new lands close to home, or learning blacksmithing will let you through nearly everything. If you don't, though, it can get very ugly. Irwin essentially spams an area of effect power that fills the entire screen. The dragons hit a bit too hard to be fair. But the worst is the Sierra and Vadise fight. Large area of effect powers, some of which cause the player to fall asleep, nasty amounts of health, and you can only bring one ally where you'd normally get two. Even better, they get back up if you don't beat them both at the same time.
Tropicallo is pretty ridiculous. You can only damage it by destroying two flowers which respawn at a set rate, and one of these flowers has a self-destruct with a large range — one corner is usually safe, but if you're unlucky the flower can get slightly out of position and blast you anyway. On No Future, the hardest difficulty level, this fight goes from "hard" to "utterly insane", as the explosion is a one-hit kill on just about anything, even from 999 HP, and Tropicallo's life bar is huge.
Demon Droguza from Arc the Lad: Twilight of the Spirits. He has physical attack power that's through the roof, and has ranged attacks as well - a sweeping tail laser that slices across the midpoint of the battlefield (where you will be caught, unavoidably) and a giant energy ball that goes boom on your little cluster of fighters and nukes roughly half of their HP on a normal, non-grindfest playthrough. And your healer will very likely die. Add in the fact that the resurrection spells aren't likely going to be available to you at this point....
The final boss of Arc The Lad II; the Dark One is the hardest boss in the entire game. He's so strong that, unless you have a powered up Choko in your party, you're going to have to level grind a ton if you want to even be able to scratch him. It's not recommended to take him on with a party below level 100. You can also expend 2-3 hours of real time constantly buffing Elc and Gruga over and over before taking a single swing each at him and then running back out of range to repeat the process until he dies.
The Huff 'N Puff fight from Paper Mario. Huff 'N Puff is a giant cloud, and pretty much every time you hurt him with your jump or hammer, tiny little cloud baddies would pop out of him. If you didn't get rid of the tiny clouds by his next turn, he would swallow them up and heal himself. Often there were six or seven tiny clouds that couldn't all be removed by the next turn. Also, he had a devastating electric attack, and often charged himself up so it would shock you if you jumped on him. Truly one of the more irritating bosses in the game.
The Crystal King is no slouch. He doesn't really rely on one gimmick, either; he has a powerful healing move that can undo multiple turns worth of damage (which he can spam), he can split into copies, and his attacks really hurt (one can even freeze, taking Mario out for 2 turns at a time).
The Lava Piranha has two forms, making it twice as hard to beat. Its first form can hit reliably hard, and takes a while to kill. One you kill it, the battle seemingly ends until the thing bursts out of the floor again. Now, it's gotten a significant power boost, even more HP, and is on fire, making contact attacks impossible.
Unless you use Sushie's Ultra-Rank attack, in which case the second part of the fight becomes much, much easier.
Jr. Troopa can get quite tough in later fights, mostly by changing his attack styles radically. Some of his forms include growing bat wings and a spike on his head, making him immune to conventional hammer and jump attacks, and getting a magic wand, which lets him hit tremendously hard.
Cortez is often considered one of the harder bosses. His health seems low at first... until you realize that he has three forms AND gets a free health refill in the third form, meaning you have to deplete his health bar four times over. His first form is easy, but his second form has a nasty charged attack that can take out large chunks of valuable health. This pales in comparison to his last, and longest, form where he hides behind his four floating swords which all attack you at once, meaning he can land five attacks in one turn if you aren't careful.
By the way, the floating weapons all count as spiked enemies AND flying enemies. This means none of your partners can deal damage to them without special moves, and only three of them can damage Cortez while the weapons remain (Mario's hammer doesn't work either). So you had better pray to God that you have Spike Guard (allows Mario to jump on Spiked enemies) equipped or you're screwed. Oh, and one of the weapons can poison you and almost all of them have fairly tricky timing for their attacks that makes dodging and preventing against that poisoning difficult (due to the relatively low amount of HP you get in this game, poisoning is a very serious problem).
Gloomtail in the Very Definitely Final Dungeon is a real nasty thing that you'd only know about in passing if you bothered to listen to the storyteller, as otherwise the encounter with this beast is a shocker. This battle doesn't have any special gimmick to it, he just hits real hard. This guy has a lot of HP, has several, very powerful attacks and good defensive power. Several of his attacks (particularly his earthquake), are very difficult to dodge, and Goombella outright tells you to use Vivian's Veil to completely avoid his MegaBreath, which is extremely powerful. Your HP will constantly plummet troughout the fight, so players shouldn't be shocked if they end up using half their inventory healing all the damage this guy does.
The Final Boss, the Shadow Queen, is also particularly nasty. Excluding the Bonus Boss, it has the highest HP count of the game (150. For the record, neither of the previous bosses ever broke 80 HP), it has flunkies in the form of its hands, which possess an extremely annoying and difficult to guard attack that drains your HP for the boss, it can inflict various status effects (including poison and infatuation), it can boost itself for a while and it can get as many as 3 attacks in per turn because of its hands. The hands themselves have low HP, but they'll just keep reviving every turn if you keep killing them, which is practically mandatory as the boss hits hard enough on its own. This results in a long and arduous fight in which you play the role of the healer that ocassionally pitches in while you support a Partner with multi-targetting attacks (preferably Vivian for her Fiery Jinx).
Paper Mario: Sticker Star: If Megasparkle Goomba put up the points that you need to use the Battle Spinner and a boss's weakness to fight effectively, Tower Power Pokey hammers in these points with a sledgehammer. You thought Megasparkle Goomba's 90 HP was crushing? Try 300. With sky-high defense to boot (7, in a series where any defense score is notable). Firstly, each turn after the first he can't be hit by hammers. Then, after he's fully emerged from the ground, he'll summon green Pokey flunkies (and do it again occaisonally). His spinning attack is hard to block completely, and his falling attack has a chance of crumpling you (essentially complete paralysis) for multiple turns if not blocked. And he can heal himself for 10 HP at a time if he so desires. You essentially can't defeat him without using his weakness; even then he's a tough fight. And the bosses get harder yet.
The final boss, Bowser, is a horridDifficulty Spike from the previous boss(es), and that's saying something compared to the standards for boss fights in this game. He has an absurb amount of HP, insane defense, and a whopping five phases. He's spiked, so if you favor jumping stickers, better learn how to time your hits with the hammer or you'll have to buy a lot of Super Boots. All of his regular attacks take off 10 HP unguarded, and his jump attack can crumple. You will not beat him without having an entire inventory full of high-power stickers and frequently use the Battle Roulette with pinpoint accuracy. Even if you do, you'll have to take along the Thing Stickers that will weaken him, or you won't last beyond the first phase. Even then, each phase drags on forever, and you'll never know when the next one will start.
The first phase summons three flunkies. Because of the choice of flunkies, very few stickers will take out all three at once. On top of that, whenever one's killed, even more are summoned.
The second phase has a giant Thwomp. Whenever it's up, Bowser will take only 1 damage from anything. It also hits twice for 10 damage, on top of Bowser's barrage of attacks. On top of that, only one kind of sticker will knock it over and make it vulnerable to Thing Stickers.
The third phase, Bowser uses only one attack, but it's a doozy. He summons a barrage of fireballs which are impossible to block completely. Using the proper Thing Sticker won't work permanently.
The fourth phase can be ended in one move, but if you can't, you'll have to deal with an invincible enemy in front of Bowser.
The final phase? Hopeless Boss Fight, yes, but his attacks hit for horrendous amounts of damage. The third move is a devastating combo that will crumple you for 3 turns if you get hit with the final blow, at which point you can just shut off the 3DS. Oh yeah, and his fire attacks can destroy your stickers. It's like the developers wanted players to suffer in this game.
Breath of Fire II certainly had a fun one in the form of Barubary. He's statistically the strongest enemy in the game (this includes the final boss, by the way, never mind that said final boss is freaking GOD). And to get a clue about the Infinity Plus One Accessory location, you have to face him alone. With no reduction in his stats. You do get free healing before the fight though if you do so.
Algernon and Wildcat definitely count as well. The main problem is that the Outside-the-Box Tactic for beating them is a massiveGuide Dang It in both cases. And in both cases, when you're having trouble with said bosses and check a guide for them... you realize you missed your chance. Tough luck.
Guardeye is a bit of an odd case, as if you're using a guide (which would be understandable, given all the Guide Dang It this game has to offer) he actually becomes harder. Why? Because you need to spare the old man in order to get the best ending. This means you can't use your strongest attacks, as nearly all of them hit every enemy, which will kill the old man. Hope you have some very powerful healing, since the eyes can easily wipe you out in a few turns if they're all alive.
Orjugan, especially on Hard and Nightmare. It can only be damaged by playing tennis with its bombs, or with the Flame Sword magic, has highly-damaging Combat Tentacles, a deadly super laser blast that is difficult to dodge without taking hits from the tentacles (which can kill you instantly on higher difficulties), and finally, periodically summons shadow creatures (which you need to equip the Rainbow Fragment to kill).
The vampire demon boss (called Vagullion in the PC remake) in Ys Book I and II. He starts out as a swarm of Goddamned Bats that home in on your position and coalesce into his true form, often faking you out. And if you don't hit him at just the right moment, you'll take a ton of damage from him, making him a bit of a Luck-Based Mission. In the remake, Khonsclard (the rock monster) and Dark Fact are even more cheap bastards. To say nothing of the bosses in Ys II Eternal/Complete, which are often Bullet Hell (in an RPG!).
Gaia Online's MMO, zOMG! has a few. First up is Katsumi's Kokeshi Doll. She's far, far stronger then the already nasty Kokeshi Dolls wandering about Zen Gardens, which wouldn't be a problem if not for the fact that she will always attract a horde of these lower-ranked Demonic Spiders as you try to kill her. By a horde, we mean about a dozen at a time, with more coming in every couple seconds. Oh, you've got area affect attacks? Well, watch out for that Pink Fluff! Oops, you hit one? BOOM!
The Battle Of The Three Bridges. You fight three Nexus Animated, which are much stronger versions of the regular Animated roaming the gardens. Both are assisted by two normal Animated. The Kokeshi Nexus is arguably tougher than Katsumi's Doll. The Drum Nexus can play kickball with you, and has a nasty AoE attack. And the Lantern Nexus is way tougher than any of the other enemies in the area, and only spawns at night. (Meaning if you don't kill it before the sun rises, you have to wait an hour for it to respawn again.) And if you get too close to the edge of the bridge, there are still exploding Fluffs.
Stone Coatl is the definition of That One Boss. He takes all the annoying bits of these previous fights and turns them up to eleven. The fight starts with Tiny Terrors and Witch Doctors, the second of which can heal their allies and slow you down considerably. After each wave of Animated, you fight a Mask of Death and Rebirth, which could qualify for this trope in their own right, despite being "mooks". And the last wave of monsters before you even fight the boss itself are Bladed Vases which have a ridiculous area of effect attack that deals heavy damage in a circle to anyone even kind of sort of near it. Oh and if you don't work fast, the vases can easily wipe out a party because they keep spawning until a certain number is reached. Finally, when you reach Stone Coatl, he has the most HP out of any boss you've fought, has several different attacks, one of which knocks you back across the entire screen when you've been to close to him during the fight, and he spawns an infinite number of Animated which can be any or all of the types previously mentioned. Stone Coatl is easily harder than the final boss.
City of Heroes has a few Archvillains and Elite Bosses who give players fits, depending on what powers the players or team have. Defeating them often requires copious amounts of skill and luck, or at least more skill and luck than the game normally needs.
Frostfire is probably the first Elite Boss newbie heroes run up against, making him a sudden brick wall in what was previously a very soloable game.
Nosferatu has an auto-hit Negative Energy aura that drastically reduces your to-hit chances, which stacks with his own attacks that do the same. Oh, and he can heal himself too.
For villainside, Positron can hit through high defenses with Energy damage, slow your attacks tremendously, and is loaded with plenty of area-of-effect attacks.
The Statesman Task Force version of Captain Mako and Ghost Widow are often complained about. Apart from being artificially toughened via level differences, Captain Mako has a Limit Break that makes him nigh-unhittable (without Status Buffs), while Ghost Widow can heal herself based on the number of players in melee, and break through just about any status protection available.
The Carnival archvillain Madame of Mystery is not fun either. She's heavily resistant to most kinds of damage, requiring the use of a temporary power to defeat; on top of that, she can quickly floor your endurance, leaving you helpless.
Also, Kadabra Kill. Multiple mezzes, a healing aura, and a pet.
The Reichsman, the final boss of the Issue 15 task forces. He is literally in a class of his own, "Reichsman," requires a very specific strategy to take down, you'll have to fight four other Archvillains either right before or as you're fighting him, he has some of the most powerful resistances in the game, and the battle can, depending on the team makeup, take anywhere from twenty minutes to several hours, because he has one of the highest HP totals in the game: 200,000+ , over ten times the amount of normal Archvillains. Alternatively, if you're a villain, you won't have to face four adds of Archvillains, one at a time- instead, waves and waves of minions, spawning immediately after each other, will rush the players, causing them to have to fight an average of four groups of normal enemies at once, as well as Reichsman. Did we mention that every minute, Reichsman lets loose a stun attacking your entire party that will temporarily knock out anyone, no matter how protected, that it hits?
But hey, maybe being a villain is for you. In that case, in the release-date final showdown for villains, the Lord Recluse Strike Force, is going to be Fun. Rather than fighting five Archvillains (now relabeled Heroes) at once, with the Archvillains entering the fight one at a time as Reichsman's HP lowers and he summons them as reinforcements, you get to fight eight Heroes at once, who are all three levels higher than the Archvillains in the Reichsman Task Force. Not only that, these eight Heroes have special code that causes them to stick together, stymieing any attempt at separating them so they can be defeated one at a time. Furthermore, four of those heroes are ostensibly Defenders, meaning that they either layer buffs on their already insanely powerful allies, or debuffs on the overmatched players. Finally, the leader of them, Statesman]], will, when critically injured, render himself either completely or 97% immune to non-psychic forms of damage, and attack the entire party near him with a devastating blow that would kill weaker archetypes outright if not for the recently-added code causing attacks that would be one-hit kills to leave the player with one HP every eight seconds. Even with upgrades in power for characters since the LRSF came out, it's still an incredible challenge, and not something that can be cleared by most teams that don't prepare an exploit allowing them to fight the Heroes sequentially rather than in parallel.
And for those of you who are still gluttons for punishment, there's the endgame, containing Director 11. Director 11 isn't that hard- he's only a level 54 (meaning that level 50 characters, at the cap, will deal 44% as much damage/debuffs/stun duration/whatnot to him as they would to an even level enemy, and he'll deal 144% damage/debuffs/stun duration to you) Archvillain, normally a tough fight but easily doable. Unfortunately, thirty seconds after you fight him, he creates invisible, intangible, untargetable pets who drop stealthed (visible with perception powers) Proximity Mines all over the warehouse where you fight him. Three seconds after someone stands near a Proximity Mine, it detonates, dealing roughly 20% of a Tanker's maximum HP. And he creates more of these invisible pets as the fight goes on, more every thirty seconds, so that it's easily the case that if you let the fight last long enough, you will be unable to stand in any part of the warehouse without triggering at least three proximity mines. Oh, and there's a badge for defeating him without getting hit by any of his Proximity Mines. Not killed. Hit.
Battle Maiden is no slouch either. Also a level 54 Archvillain on her own, her signature ability causes patches of blue fire to erupt from the ground, one-shotting anyone who stands on them. These patches can spawn in midair, but are easily avoidable. ...Except for the fact that you can't move while using most powers. These patches spawn constantly during the fight, and are hard to see with low graphics. At least the badge is easy to get...
Primal Col. Duray is like a lower level version of Battle Maiden. You fight him in a Dual Boss fight with his Praetorian Counterpart. While Praetorian Col. Duray is tougher, and hits harder, Primal Duray is just annoying. He periodically calls in Air Support (killing anyone standing on one of the mercifully small patches for too long), and has a tendency to teleport all over the multilayered battle field while his counterpart is alive, making it insanely difficult to keep up with him.
Treasure of the Rudra: Soma, due to the fact you have only 3 allies and you fight him after clearing several fights in a row leaving you weakened and depleted of MP. Laumen has a high defense stat, Mantras won't do jack squat on him.
Wizardry VII: Crusaders of the Dark Savant: Magna Dane and the Lord of Dark Forest can be extremely challenging if you aren't well-prepared. Magna Dane uses some of the most powerful damage/instant death spells in the game, is immune to most magic, and has a remarkably strong physical attack. He can easily wipe out the entire party in one round. He's also backed up by up to 8 High Fathers, who are all almost as strong as he is. The Lord of Dark Forest is lightning fast and hard to hit, can instant kill your party members easily. He's backed up by a large group of condition spamming Monks and Ninjas who can also do instant kills on your party. He'll occasionally summon a Godzilla monster, which is strong enough to wipe out your entire party on its own unless you are extremely overpowered. And on expert mode, there's two of him.
Gates of Hell seems to be That One Boss in The Last Remnant. It has 2 free attacks that it can perform while it's in its turn, both which can hit all the deadlocked teams (it has multi-deadlock), not counting its attacks in its main attack phase, which means it can attack 3 times in a turn. The problem is that a lot of players will try to deal as much damage to the boss as possible, causing nearly all your teams to engage in deadlock with the boss, which will result in massive damages being dealt to nearly everyone. And if a group is dead, the boss will cast Pandemonium, turning the dead group against you. The best way to beat it is to keep only few teams to engage it, and let the rest acting as healers and rotate in if possible to maximize the survivability.
Phantasy Star IV had Lashiec, who probably was the single most difficult fight in the game, even more so than the final boss. The fact that he appears in That One Level, after a miniboss fight and Marathon Level that virtually seems designed to screw the player out of healing items does NOT help.
Eternal Sonata's first fight with Captain Dolce is not to be underestimated. Encountered after being separated from the characters that you have to use in her ship for an extended period, you're likely to be underleveled and Dolce will wipe the floor with you if you aren't prepared. She's faster than greased lightning, and packs a wallop and a half. Top it off with the fact that she comes with a pair of henchmen that will heal each other if you don't kill them in one go and do some decent damage themselves.
There's also the second fight against Tuba, which is a bit of this and a bit of Wake-Up Call Boss. Bosses prior to him were no pushovers, but Tuba has the ability to kill characters in one turn if you don't block consistently. Possibly even multiple characters in one turn, since a couple of his attacks hit sizable areas. He can also heal himself for large amounts when he gets to low HP. Oh yeah, and the fight also requires you to use Beat in your party, so good luck if you haven't been leveling him up and keeping his equipment current.
Pretty much every human boss except the first Tuba fight and the PS3 exclusive fight with Fugue can count. All of them have a tendency to run behind you so you can't block, and if you fail to block one of their attacks, you can't block any subsequent attacks with small block windows either. Also, all except Frederic have multi-hit abilities with small block windows that can and will instant KO even your tanks.
In The WitcherIn the proper fight at the end of chapter 5 Azar Javed qualifies. He will regularly blind or knock you down, both will disable you for a significant period of time, only one of the two can be properly defended against (willow potions prevent knockdown), blind can only have its effectiveness decreased by spending a talent on an ability that stops it from working sometimes (and no other enemy in the game seems to use blind and silver level talents aren't something you throw away...). To make matters worse, if you made certain choices in the game, this battle has an escort who will die if you lose the bosses attention and he starts to attack them (Berengar is really Overrated And Underleveled) and you have to start over if you want to save him (admitedly, this doesn't get you anything). Also, one of the early bosses in the game, The Beast, is well named.
The Beast himself is easily stunnable for instant kill. It's his pack you should worry about. Then again, you can get those packs anywhere. If you're really not careful.
And his lag. The fire graphics for his fight are significantly more graphics-intensive than basically anything else in the game, so (unless you change your settings) you have to deal with framerate issues while you're being mobbed by respawning Demonic Spiders.
The Witcher 2 has two horrible offenders: the first is a draugir and his three lackeys. This fight would normally be a cakewalk, except that Geralt is now possessing a ghost (long story) WHO CAN'T DODGE, or use magic like the kinetic barrier (defends against one draugir spine-breaker) Quen, or even feel the effects of the strengthening potions Geralt just drank thirty seconds ago. And worse still, the small army that is supposed to help Geralt-Wraith defeat the draugir is so weak that the enemy kills them as if they were tearing paper! The key is to use parrying, but if you haven't allocated points in Geralt's Swordsman tree, you're screwed.
The second is a secret boss. To explain with a few spoilers, he is a mage who launches heavy-damage fireballs in rapid succession, and can also form a Quen barrier around himself that lasts continuously for about ten seconds. The fireballs are fairly easy to dodge... until the mage summons two stone mini-golems (he can do this three times total). Said golems are over-powered and extremely agile, and can kill the player in one second while the player is switching Geralt's swords. These mini-golems are extremely dangerous, harder to kill in pairs than in singles, and to top it off the mage is still throwing that heavy artillery at you!
Mario & Luigi: Superstar Saga has the Piranha Mom, who is not only tough herself, but spawns two smaller piranhas. Which wouldn't be so bad, except the only way to win the battle is to attack Mom directly, whereupon the two smaller plants both spit fire/lightning at both Mario and Luigi. There's no real way to predict which brother is going to be attacked by which plant, unlike every other enemy in the game up to that point, and the attacks seem to vary timing to make them hard to dodge? Mom regenerates health, and creates new Piranhas any time the old ones die?
Trunkle. The thing has crazy defense, so that your moves which do twenty to thirty damage to normal enemies does... 3 damage, maybe 6 if you get a Lucky shot, on him. Plus every other turn, he'll inhale enemies to heal himself, and do damage to you if you don't jump properly. Eventually he breaks apart, but that's not the end of it - he's now four tiny Trunkles, and if you don't guess which one is the real Trunkle and defeat it first, he reforms and you have to start all over again! Attacking the tree on top of his head does shorten the battle, but it causes Trunkle's defense to skyrocket.
The Bean Piranha. It has a very low HP count for a boss, but it more than makes up for it by the fact that it has insanely high defense (like plenty of bosses do in the late game). This is because you're facing it on solo with Luigi, who is the slower and offensively weaker of the two bros. Trying to take it out with anything other than Thunder is suicidal. Getting hit once by this guy probably means you'll have to waster your precious turn to heal, and unless you smart up and spot the differences between the two versions of his attack, you'll probably get hit again and have to waste another turn to heal. This fight can feel like a Marathon Boss simply becaue of how slow progress is made, and it doesn't help the fight comes out of nowhere.
Mario & Luigi: Partners in Time is generally rather easy for a Mario and Luigi game, but its final boss plays this straight. A) it is Nightmare Fuel incarnate for Mario's target audience; B) it is comprised of seven different targets—though thankfully you only need to attack three of them; C) it, unfortunately, has incredibly high defense for those three targets you need to hit; D) those three targets need to be attacked in order, otherwise you won't make any progress; E) only the final target's HP counts, the previous two need to be disabled just to expose the weak point, and they can and probably will revive; F) it has powerful attacks that can take down one pair of Mario Bros. with ease; and G) it comes after two other bosses, who—thanks to their high HP and powerful attack—can easily make you use up a lot of your healing and Bros. items. An even-leveled player can easily spend upwards of twenty minutes to half an hour on this final battle. An underleveled player... well, let's just say it balloons into full-blown Marathon Boss territory.
And of course those bosses had their HP lowered in the Japanese release.
Mario & Luigi: Bowser's Inside Story continues the trend with the final boss, Dark Bowser and Dark Fawful Bug. Now, neither is difficult to dodge attack wise, not particularly hard to damage, but they take forever to kill. First it's Bowser vs Dark Bowser, then at 1000 damage he heals, throws a whole bunch of enemies, you have to dodge pretty much all of them and said boss himself to reach him, then hit his stomach, then suck up the Fawful Bug... and Mario and Luigi THEN get their turn. The bug thing itself has three legs, two glasses and the Dark Star as targets, so Mario and Luigi have to destroy all the legs and the glasses to reach the star... get about two turns of attacks against it, then it repeats from the first Bowser phase.
One of the toughest bosses for Mario and Luigi is midway through the game when you reach Bowser's brain and fight copies of yourselves called Memory M and Memory L and yes, they are hard. Remember in the old days how cool it felt to grow to Super Mario or Luigi, or to get a Super Star and become invincible and run through your enemies for massive damage? Well that's about to bite you in the rear pretty hard when these guys do it to you constantly through the fight, which means if you're not good at perfectly dodging or countering attacks at this point, you're pretty much screwed. Also for more fun, their stats are similar to yours, meaning that Memory M is offensive with more speed and Memory L is defensive with more health. Memory L also doubles as the medic, so if you knock out Memory M, he will just revive his fallen brother. Naturally, you would think to defeat Memory L first to prevent him from recovering his brother, but that's easier said than done since he's based off of Luigi, who hates to fight, he will often run off of the screen until his brother faints and remaining completely invulnerable until he returns to the battle. This fight is usually the most remembered in the entire game, not just because of a nostalgia factor, but also because of how difficult it is.
The Junker. It seems like a standard Flunky Boss, but then he sucks Luigi up and sticks him inside one of the Junker Cans. While Luigi is in the can, you have to keep track of which can holds him and destroy it. All the while, the Junker and the cans are hitting you with powerful attacks, as well as the cans frequently swapping Luigi around. Also, the cans have at least three turns worth of HP, and if Mario goes down, the battle ends. Also, by the time you finally get Luigi out, he's almost guaranteed to do it again. Did I mention that's one of the few attacks in the game that's completely unavoidable?
The Fawful Express. It's only attackable with the flame attack, has a semi turn timer you need to defeat it in, the mountain halfway through also becomes a giant mech and there are at least four different attacks to dodge. Since the flame attack is controlled by the DS microphone, it can be difficult to get full damage on your attacks, and the train likes to heal while it's in the mecha. Also, since the flame attack involves blowing into the microphone as hard as possible, you're going to end up pretty darn lightheaded which makes focusing harder.
Every boss can feel like this (some more than others), along with Marathon Boss, if you're going for a Challenge Medal run. The Challenge Medal is an optional equipment piece that highly increases every enemy's stats, but increases the coin prize at the end of each battle by 1.5. Combined with a low-level run (in order to get the Easter Egg at the end for doing so), this can take already hard bosses' difficulty to ridiculous levels, also making Gauntlet battles outright Unwinnable because of their turn limit. Note that the Medal also affects Bowser, who has it worse because he's on his own. Using the Medal, unless you're an expert at dodging/blocking everything (and really, you should be since you're the one who decided to go full-game with it), then you're in for quite a few moments of frustration. Enjoy the Junker.
Torkscrew has a ton of HP for the point in the game you fight him, and he has several attacks which are long and drawn out. Jump at just the wrong time during his digging attack and you'll have to chase him down for half a minute while steadily losing coins and jumping over mines. He's also got a spinning drop which is hard to counter, does terrifying amounts of damage (say, 40, when Luigi's HP may not be above 70), and has a good chance of lowering defense; if Mario is hit, he won't survive much longer. And he will sometimes chase one bro into the background, which forces the player to multitask because enemies will attack the other, in addition to Torkscrew himself. If that wasn't all, he can't be jumped on. This is only the third area's real-world boss, by the way.
Thunder Sass might count for this title. His attacks hit very fast and hard and can cause dizziness (which is basically paralysis in the series), plus his minions make it harder to avoid an attack too. Think you can spam your powerful attacks to kill him? Nope, because the gimmick of this fight is you are not allowed to use any sort of attack (including items that affect enemies) and must counter his attacks to hurt him at all. You can't even use badge effects to heal yourself without using items, which is a real pain in Hard Mode since you're only allowed 10 of each item. And the kicker? This is pretty much a miniboss, as you need to beat him to fight Big Massif, which is another That One Boss (see below). That's just cruel.
Heavy Zest, another miniboss you need to beat to reach Big Massif, is another pain. Not only does he hit very fast and hard, like Thunder Sass, but the tells for the attack where he rushes off stage and charges into you are very hard to figure out. But that's not what makes him difficult. No, it's the fact that there is a turn limit on this fight. You get three turns. And it doesn't end when you beat him. No, you have to defeat his minions as well. Hope you've figured out the Luiginary Attacks by now.
There's Big Massif, who gets an attack boost whenever you kill his minions. Problem? Due to the Dream World's mechanics, all of your attacks, regular or Luiginary, are going to at least hit some of them.
Wiggler would normally be a tolerable fight... if Popple wasn't involved. Every now and then Popple will try to attack Wiggler, and if you don't attack him twice in the same turn with both Bros., then Wiggler's already strong attacks will hit even harder and become harder to predict. Only problem is, if you're having to use 1-Up Mushrooms to revive constantly, there's no stopping him. And even then, sometimes you can't stop him. During Wiggler's normal charging attack, on the rebound, Popple will cling to the one targeted, which gives jumping to dodge Wiggler a massive delay. For Wiggler's enraged charge attack, it's very hard to dodge and takes off giant chunks of health; and if one Bro. gets hit, then Popple will trip the other, forcing them to be hit unless they jump at precisely the right time.
And guess what? After whittling down Wiggler's quite high HP, Popple attacks. With no break from the last fight. His attacks are tough to counter and the tells are short (especially when he kicks a brick block, then sucker-punches [erm, kicks] the projectile into you and does even more damage). If you miss his spinning attack, then he hits you with a deadly uncounterable attack. Expect to burn through a lot of 1-Ups, and it's oh-so enjoyable to see Wiggler chasing off Popple.
Earthwake, the third giant boss, who can turn into a flying hammer at one point and repeatedly strike at Luigi (which in itself is That One Attack due to how hard it is to block/counter). He can take you from literally full health to zero before you can move if he uses this attack, and on Hard Mode he uses it repeatedly.
Pi'illodium, the guard of the Pi'illo Temple in Somnom Woods. This boss not only has a machine gun equivalent laser attack which you somehow have to memorise the pattern of in about 10 seconds, but also one that has him fly off screen and come smashing down on a bros head, with the timing needed to dodge it being both split second and mostly blind. It can also chase after Mario and Luigi while firing a constant barrage of missiles, heal itself on a regular basis and activates a deadly self destruct timer when near to death (which can act as a Kaizo Trap).
Kamek in his final boss battle, since he splits into four clones, all of which have their own attacks, can heal each other and boost each other's attack stats.
Giant Bowser, since the battle is both a Marathon Boss filled with precision dodging and requires the gyroscope in at least two different phases (the gyroscope isn't particularly accurate at the best of times and it's used here in situations where failure is basically a One-Hit Kill).
Antasma (final time), since his attacks all have a chance of putting Mario to sleep, causing him to lose a turn (in the Battle Ring) and have to escape a deadly gauntlet of saw blades and pits to try and return to the fight.
Dream Team also has the Zeekeeper. Not so hard when the battle works, but way, way bad when you're on Hard Mode with no way of healing (outside wasting one of the two turns you actually get to attack him in) or when the motion controls in the zero gravity section fail to work altogether due to a Game-Breaking Bug. Or when you're on Hard Mode AND the motion controls fail, in which case you might as well as consider yourself cursed. Oh, and near enough three quarters of the battle is his turn. How? Because he always runs away, and you have to catch him to attack yourself. Which happens after between two and four of his own attacks, all in a row.
Made worse by how you can FAIL to catch him, at which point he mocks you and flies into the dimensional rift again, giving you no chance to fight back for a while.
Dream Team also continues the trend of the final boss being ridiculously difficult for the game. First of all, its arms need to be incapacitated for you to being able to target its weak spot For Massive Damage. Second of all, it hits hard with all of its attacks, and they're hard to avoid. Third, it can summon enemies in amounts that is restricted to the Dream World enemies/bosses, and while the enemies are on stage, the boss retreats to the background to heal itself AND its arms. Lastly, it can summon a background enemy which takes an ungodly amount of hits/counters to finish off. Even with the best gear and the best Bros. Attacks, this boss will likely mop the floor with you. Repeatedly.
Spirit User Tuoni and Wicked Witch Olly in Chapter 6 of Avalon Code. You remember all the ass-kicking weapons and armor you had back during the Inevitable Tournament in Chapter 5? Yeah, you have none of that now. Same goes for the spirit magic, property manipulation powers, and even the ability to heal. One of them is a remixed Chimera with limited intangibility powers, and the other has taken her meds since your last fight against her. Genkai said it best: "Best of luck, I hope you don't die."
The final boss of the EverQuest expansion Gates of Discord, Tunat'Muram Cuu Vauax, was this for the whole player base as he was not killed until well after the next expansion came out.
EverQuest II's Raid Battle against Venril Sathir qualifies for this in spades. Not only do you need 2 copies of the same item from a previous raid mob to even make him DOABLE (thankfully they aren't consumed by the battle), the fight is simply unforgiving of ANY mistake. Guy on statue duty lags? Everyone dies. Someone doesn't cure their poison? Everyone dies. Someone casts too much/not enough? Everyone dies. Venril Sathir decides to screw you by giving the same person both his curses at once? Everyone dies. Someone crosses the threshold of his room too soon? Everyone dies. Venril is the raid mob in EQ 2 responsible for more raid guilds breaking in half than any other. The kicker: He's not even an end of progression boss, he's in the middle of an expansion's progression.
Venril did eventually get nerfed. EQ2 generally nerfs the high end raid bosses about 3/4ths of the wait until the new expansion to give the less uber guilds a better shot at getting them down. See also: Perah'Celsis (raid version) in the most recent expansion, who was changed so he no longer charms the tanks making the fight easier.
Also from EQ2, the Leviathan. Even though it is a level 80 raid monster, and the max level is now 90, people still refuse to go anywhere near it for several reasons. At level 80, it would reflect spells up to level 87. This meant mages were near useless for DPS, and any group Debuff's cast by bards could turn around and hit you. You also needed at least 100 noxious potions to cure yourself. Then the time it took to kill. Guilds would often have to spend a week or two before farming fluids which you need to blow the mob up from the inside. And at the time, you needed to kill him to be able to access Veeshan's peak, and get your Mythical weapon.
He also resists the holy element, so that holy elemental Infinity+1 Sword you had been using to slice through pretty much every other enemy in the game won't help
Skies of Arcadia has Recumen, the Red Gigas. While he is technically a Hopeless Boss Fight, you are expected to survive the encounter with him for more than a few turns, which is difficult enough. And after him, you have to fight Belleza in ''another'' ship-to-ship battle; this time, you DO have to win. You better have brought plenty of healing items for your ship, despite not even having a ship right before these events occured.
The Bonus Bosses added in the Legends version all level up with the player (and exponentially at that), and are balanced under the assumption that the player will be taking advantage of otherwise Game Breaking moves like Delta Shield and Justice Shield. This can make them seem nigh unwinnable to a player who isn't aware of those strategies, and even with them they're still pretty challenging.
The Phantom Evil King (Epros) from Okage: Shadow King. Say goodbye to every Black Cat Jewel you might have owned, and if you don't have Big Bull with at least his second-level fire attack and a bunch of help from Stan, you'll be stuck here a WHILE. It's especially sad when a fight that ends up being harder than the final boss is against someone who ends up joining your party.
The roguelike Iter Vehemens ad Necem (aka IVAN) brings us the apotheosis of all bastards: Ischaldirh. His stats are pathetically low even compared to other bosses in the game. He has, however, access to the most frighteningly powerful magic in the game, and is not afraid to use it. A favorite of his is teleportation, which he uses with relish. Get close enough to split him in two? Poof, you're on the opposite end of the screen. He also is fond of teleporting your gear away, not to mention teleporting your LIMBS away. He also can summon an explosion and then teleport that explosion on to you for massive damage. His most brutal tactic, however, is his summoning. He can summon any monster in the game. This includes other boss characters as well as golems made of material that give them ungodly high stats. Also he can clone you. These clones have the same stats and equipment as you. Considering you lived to see the end of the game you're probably very high level with very good equipment, so taking on just ONE of your clones can be a challenge, to say nothing of the mobs he's capable of summoning. Beating the game is literally considered to be a glitch, and with bosses like this it's no wonder.
That One Boss of Wild ARMs 4 comes in only about halfway through the game, in the form of Hugo. He was annoying in that he would almost always decide to stop time and dodge your attack right before you try to attack him! Use lock out? He'll move to a new square. And don't even try to trap him around a lock out, because that stops you as much as it stops him, leaving you open to his attacks. His swords can become a fucking bow! The strategy—corner him with three characters; he can't get past them—is a "why didn't I think of that?!" moment, but then again, it's also not hinted at very well, if at all, unlike every other Puzzle Boss in the game.
Serious Dungeon Crawl players will come to loathe the name Sigmund, given the ease with which he slaughters players left right and centre. He usually shows up between the 2nd and 4th floors of the dungeon (meaning that you're approximately level 3 to 5 when you face him AT BEST) and comes with several nasty spells (Magic Dart, Fireball and Invisibility, all very nasty against players at this point in the game) and backs that up with a scythe (again, very nasty against players at that point). Oh, and depending on how the dungeon generates, he might just well be the FIRST boss you face.
Another nasty early-dungeon boss is Grinder, the unique shadow imp. He comes with a paralyzing spell as well as a ranged negative energy spell and pain-branded melee attacks. Undead characters don't have much trouble with the last two, but paralysis is extremely dangerous that early on in the dungeon. As with Sigmund, many people find themselves running away from him until they can level up a bit.
Later on in the dungeon, you may have the misfortune to run into Mara, a unique rakshasa. His fire bolt attack, ability to summon copies of himself, and ability to confuse you by making enemies look like something else are all decidedly unpleasant, but manageable. The real kicker is his ability to create a fully-powered copy of any other creature in sight, including yourself; your clone will have all of your best abilities and will permanently copy your condition at the time of its creation, including status buffs like Haste or Berserk. One way to mitigate your doppelganger's effectiveness is to deliberately use crappy equipment (like weilding food as a weapon) up until you get cloned, and then switch out for the good stuff, apply buffs, etc. However, that means you're stuck fighting a dangerous opponent while unbuffed and with said crappy equipment, and caster characters can't even take advantage of that because their copied spells will be as dangerous as ever.
If you played Magi-Nation, you'd definitely agree that Zet fits this trope to a T. He summons a lotta monsters that have a lot of energy and therefore take a lot of abuse before going down, despite being healed beforehand comes after a somewhat difficult boss (So you have no chance to rearrange the monsters you got), and can kill a monster in one hit regardless of their energy. Stupid Cunning Blow. Sure enough... you never get it.
Ogar can give you some trouble. She summons multiple chaos jiles, which not only can be rather scratchy pains in the arse, but can use Consume, which on top of healing them, has a chance of inflicting an instant knock-out regardless of current health.
Almost everything in the later parts of Atelier Iris: Eternal Mana. Prism has fairly low defence (although his other stats are ridicously high) and most of Amalgam's worse attacks are cancellable, so the worst of them is The Baroness, particularly because of all the minions she brings with her. Atelier Iris 2: The Azoth of Destiny has the Slaith Reincarnation, although thankfully the Shadow Stalker in Atelier Iris 3 is entirely optional (the actual game storyline shouldn't really have a That One Boss).
Gorak the Ancient (aka, Lightning out his ass) in Warhammer Online's The Lost Vale is frequently an exercise in frustration. He hits MUCH harder than the bosses that come before and after him, and will occasionally go into a trance in which he fires a series of lightning bolts at random targets. If these weren't bad enough, the bolts can chain from person to person if they are too close. Even without the chain, a squishy target taking two or three bolts in a row will frequently go down, leaving the group either short a healer or a DPS. To make it even worse, he sometimes refuses to reset after the party wipes. If this happens, it requires an instance reset and hacking through some Elite Mooks to get back to him, meaning it could be 30 minutes or so of running and clearing before you can get beaten down by another cheap shot set of bolts.
Being Nintendo Hard, Odin Sphere (which is not MADE by Atlus, but is published by them!) has most of its bosses falling into this category, but Velvet vs. Beldor and Belial is the one that has been known to drive some players to tears. To say it's a warping, spellcasting wizard (and even mook wizards are a terror and a half to fight) and a ginormous rampaging dragon teaming up to fight the character with the lowest attack power in the game is to make a gross understatement of the exact levels of evil the player faces in this fight. And then after it's over, Velvet ends up captured by the bad guys anyway, to be rescued by Cornelius later. So that's awesome.
Hide 'n' Seek Battle Monster Tactics has a potential one in Trinchula, the first Target Monster of B5. It is highly resistant to every element except fire. Since Kevin can have only onefire technique at all at the time, it is virtually required to have Kaen on your battle team, which is made unpleasant by the fact that there are two wind monsters just waiting to take down your only character with a constant chance of dealing decent damage to Trinchula. What's worse is that fire doesn't do heavy damage to anything else that is particularly dangerous, which combined with Kaen mainly having melee attacks and this being a game revolving around hiding and seeking does not bode well with the poor girl's usability in the first place. Unfortunately, if you don't have the character sufficiently leveled up (elemental multiplier includes the enemy's defense in this game, which means it won't help much at all with insufficient attack) and on your team, have fun dealing single digit damage to this triple digit HP pain.
If you don't know what you're doing, the fight with Yellowjacket or Goliath in Marvel Ultimate Alliance 2 can reach TOB status. (Both play the same-you fight Yellowjacket on the anti-registration path and Goliath in the pro-reg path. To beat the boss, you have to chip at their damage until they get stunned, and then unleash a fusion attack on them. Problem is, if your fusion attack misses, or you use the wrong sort of fusion, or you take to long to pull the attack off, the boss regains the energy you just spent the past few minutes draining. And since Yellowjacket/Goliath are giants, it's hard to hurt them that much in the first place. And when they start calling in mooks...
Flash game example: the sandworm boss fight from Epic Battle Fantasy 2. It can vomit poison (yet it itself can be poisoned) on both of your party members at once, and its tail can deal a lot of damage. That and it can stun you (which means you lose a turn) which is bad, because you need both party members or else you will essentially die instantly.
4 has the Wake-Up Call Boss from hell in the Praetorian. If you don't have a dispel handy? Consider yourself fucked, as he buffs himself up to the 50% cap, with an added crit-inducing buff on top of it, with regularity. He then tends to follow it up with a sword charge that already hurts like hell without the buffs, so, like it was said, if you don't have a dispel handy, consider yourself fucked, you'll be lucky if even one character survives that. Now, this is prime material for a Wake-Up Call Boss, but what puts him here is a few other facts: The turrets that it frequently summons include some very annoying enemies, among them the dish turret, which can land a syphon on you, preventing spellcasting for some turns. This ties in nicely with the above, as dispelling counts as spellcasting. And if you manage it this far? You get to see it charge up for a turn, and call down the freaking IonCannon on you. Hope you enjoy getting stunned for two turns while it stabs you to death with the sword in the meantime. Unless it decides to buff itself up again, in which case see above. Only good news here is you get it as a summon after you win, in which case you get buffed up like this thing used to do, not to mention having it do some serious damage to whatever poor sap you toss it at.
Tactics Ogre has quite a few difficulty spikes. If one takes the right path, you have to fight both Oz and Ozma at the same time (Along with the rest of their units). Now during the other two paths, you only fight one, and when they are defeated, the battle ends. It's much easier with just Oz because they are both rather difficult and he starts off rather close to your units. (Having a one-on-one match with Denim before they call their armies out) Let's also not forget the battle with Lans Tartare...considering he's the commander of the Dark Knights, highly justified.
Its Gaiden GameKnight of Lodis also has a few contenders, such as Aerial and Nichart.
Final Fantasy Legend II has Venus. She's a sudden wake-up call since you had Mask destroying Ashura. Don't expect to win easily, but if you know to stock up on Muskets, she'll be easier at least. Then after that, the difficulty spikes again with Odin who — like his Final Fantasy incarnations — will kill you in about six rounds, on top of getting screwed by the Random Number Generator that summons a bunch of additional enemies. (But that's what the Hyper Gun is for!)
The Remake is even more vicious with Venus as she uses Rain of Death and Funeral Blaze, which hit the entire party.
Want to know how Baramos fails at being convincing at being the final boss? Just watch him cast Disperse and kick out your party members who you probably desperately need to shake off his attacks that deal 70-80 damage to all members of your party. You better have equipped the Hero with equipment that resists his nasty attacks or you're in for a very ugly battle.
The final battle against Magic Emperor Ghaleon in Lunar: Silver Star Story Complete. He is incredibly fast, attacks twice per turn, and has an incredibly powerful arsenal of doomsday spells that can devastate your entire party in two turns flat, not to mention a 1000-HP shield, an HP-draining attack, and an instant death spell. Some consider it impossible for any player to beat him on their first try.
Mugwort has pretty high HP, high speed, a physical attack that can take off a third of one character's health, a physical attack that can take off a third of everybody's health, and a hit-all magical attack that will bring your healer to the brink of death. He's of the Wood starsign, so you can't exploit Elemental Rock-Paper-Scissors on him yet. Oh, and he knows Celestial Swap.
The Holy Sapling can deal nasty and unavoidable damage to one character, very nasty damage to all characters, or incredibly nasty damage to one character. That last one is also Wood Magic, meaning that your healer will probably die if she's hit by it. You can exploit Elemental Rock-Paper-Scissors here, but doing so causes the Sapling to summon an annoying minion.
The first boss that can be counted as "hard" is the pair of Beholder-like Hel Servants in the Hard-Mode-exclusive Dark Tower of Xervah. They are extremely durable, hit hard, and can bring each other back from the dead if you don't kill them off at the same time. Compounding this is your lack of access to really good equipment, since the best weapons and armor can only be accessed if you transmute a certain item... and the Servants guard the first prerequisite to that item. Appropriately enough, their Palette Swaps later reappear in several other dungeons as Demonic Spiders.
Wraith is possibly the first boss to break out the extremely-damaging Great Magic moves that you've been using throughout the game. His Great Magic, Gravity Blessing, comes out when he hits 50% health and really hits hard. He also has a move that hits multiple times and can lay on the hurt with magic attacks. Unless you have Holy Water of Mithra, be prepared to slug it out.
Akhetamen starts out the battle with Reflect Sorcery, forcing you to go through the two weak Undead Slaves that guard him. Once you kill them, Akhetamen starts fighting, and his physical attacks are pretty manageable. However, every two turns he likes to cast the Great Magic Seraphic Law, which will put a dent in your party's HP. He also heals himself to full if you bring him to 20% HP, so you have to hit him a couple of times before tossing a Holy Water at him: otherwise it'll be wasted. The worst part, though, is that Akhetamen comes after the end of a long and convoluted dungeon with a ton of torturous puzzles.
Before the battle with the Big Bads of both the B ending and the A ending, you have to get past his two "bodyguards". The first of them is Bloodbane the dragon, and he is tough. Bloodbane hits really hard with a single claw attack ("I'll crush you!") and then follow up with a deadly flame attack ("Feel my flame!") that hits the entire party multiple times. Bloodbane absorbs massive amounts of damage before getting really nasty: by the time you slice through half his health bar it is likely that he will start using the special magic "Gravity Blessing", just like our old pal Wraith mentioned earlier, which will most likely kill all of your characters EVERY FREAKING TIME, and he will be using it every turn afterwards. With Bloodbane, the Guts-Auto Item-99 Union Plumes combo that allows you to survive a possibleTotal Party Kill is less of a convenience and more a necessity for survival, as you will inevitably have to survive "Gravity Blessing" after "Gravity Blessing" or slog it out after Bloodbane heals himself back to FULL HEALTH. In Valkyrie Profile, your party can do insane amounts of damage (as there is no 9999 damage cap) but that does not help much when the thing has 380,000+ hit points. In comparison with him, the other bodyguard and the Big Bad himself are cakewalks.
The thing about Bloodbane is that, on the OTHER path, he's a Bonus Boss. Getting to him involves mixing up a certain type of fire to melt the blockade barring your way to him, and he's every bit as tough HERE as he is on the other path. Fortunately, he drops a pretty badass sword on either route if pummeled severely enough(which can be hard on the Golden route thanks to not having access to Shining Bolt).
Due to the fact that the dungeons appear in random order when searched, there's the chance that you'll run into Barbarossa in the Lost City of Dipan before you'll hit Wraith. He can also use a Great Magic attack, Calamnity Blast, and it will wipe out your party if you're not prepared for it (either by equipping to protect against fire or the methods listed in Game Breaker). Also, unlike all of the above examples, he shows up in every difficulty level, and you're only going to survive on Easy if your hit points are full.
Phantasy Star Zero looks like an easy run through Normal mode if you know what you're doing and keep your gear up to date. Then you get to Hard mode and you run into the brick wall known as Humilias. If you don't invent compound swears after going through a stack of Scape Dolls against the guy, you have anger issues. Here's why:
His main laser is a freeze beam. If you get hit by this, unless you have a unit that prevents freezing, you will be a sitting duck. You need to roll away before you get shot, but the spread can be murder at longer ranges. The best place to be when he fires, damningly enough, is below or behind him, where he can't aim.
His sub laser is a slow beam. It will be a pain to dodge much of anything while this is in effect, so try to roll away or you will regret it in short order. This is introduced midway through the fight, but he fires it right after the freeze beam.
He also can combine his weapons into a laser sword for a single slash if you get hit by either beam. If you are still frozen when this goes off, you are taking a LOT of damage, and there is nothing you can do about it.
He also has a punch attack that's used as crowd control. He may use it if he doesn't get you with his lasers. It hurts as much as the sword.
He is also a bipartite robot, and can split into his two halves. He's completely invincible until he recombines, and he can still hurt you.
He can also arm the floor with a variety of traps that all hurt like your mother, and you better not color in all the panels if you know what's good for you. Red is pure damage, orange confuses - CASTs, keep your Sol Atomizers handy, because confusion is annoying. He can use this in tandem with his regular attacks, which is a source of rage on its own.
Finally, as one last "screw you", when he dies his upper half drives around uncontrollably while exploding, and it still hurts a ton.
Also, the full Omega Team. First off, it's not just a Dual Boss- there's three of them, and while Earp was a Breather Boss in his first appearance, Helio tends to leave you with lots of status effects and has a nasty ice spell, and Flynn was pretty hard even when she was alone. And because they all attack in different ways, and even if you equip water-absorbing armour to absorb one of Flynn's spells, you're still at the mercy of Random Number God, since she's prone to spamming Comet Slash, which leaves your party in such a devastated state that it requires so much healing that getting in any hit at all is hard, and you're likely to run out of healing items and mana before they go down.
The Lord of the Rings: The Third Age has some pretty easy enemies and bosses... until you reach the Bridge of Khaza-dum and join Gandalf in his face-off against the Balrog. Showing why everyone was afraid of him in the movie, the Balrog proceeds to open a can of whoop-ass on your party, with two powerful attacks that hit everyone and deal Fire AND Shadow damage AND drain your ability-using points, his flame sword and flame whip that hit only one person for HUGE damage, having a high evasive stat, very high defense, and more health than all of the previous bosses combined. The only character in the party who can do any appreciable damage to him is Gandalf; the rest of you are there to heal, buff the party, and be mangled.
Once you encounter the Final Battle against the Witch King, you understand why even Gandalf the White is worried about him. Having the best stats in the game BAR NONE, only slightly lower HP then the Final Boss, being able to counter you if you DARE attack him, AND having a hit-all Life Drain so powerful, 2 in a row is a guaranteed party wipe out. Just for kicks, he also can stun a character so they can't move, good luck if he does it to your healer.
Super Robot Taisen OG: Endless Frontier gives us Kyon Flaurion. Kyon comes with two Joker Soldier sidekicks. All three of them have Shields, which means your first attack is more or less meaningless. But, unless you can keep them very high in the air (hard to do with Suzuka, who, as the fastest party member, always goes first), they're also the first enemies to truly abuse Forced Evasion, meaning your attacks get cut off. The Joker Soldiers can hit multiple party members, and also inflict Freeze and Stun with monotonous regularity. Kyon, meanwhile, does one of two things: either she attacks one party member with a long, unbreakable attack string, which is basically guaranteed to kill them, or she uses her Overdrive (at will, mind you), "Bronte Magic", which hits three people and can Freeze, Stun or Paralyze. Did we forget to mention you only have one worthwhile multi-target healing spell? And that in order to use it, you usually have to break your combo so that the character can access the menu?
Mass Effect 2 has Praetorian, an exceedingly frustrating boss. First, it's a flying tank that can fire a powerful laser beam at you, and often only you, with perfect accuracy. It has a barrier that is difficult to bring down before you can even begin to deal damage to it. Once you take that barrier down, it will wait a few seconds and then slam itself into the ground, setting off a shockwave that stuns anyone nearby. Once the stun wears off, you have only a second to get away before the boss sets off an energy pulse that is almost always a one-hit-kill to anyone within a few yards. Then it will rise back into the air with its barrier fully recharged. The final kicker? It will always slowly float towards you, so while you're hiding under cover to keep away from its laser beam, it's getting closer and closer to getting you with the insta-kill energy pulse. For a game that is mostly tough but fair, such that if you die you'll know what you did wrong and how to do better next time, Praetorian suddenly crosses the line between challenging and Nintendo Hard.
It also features a couple fights on foot with enemies that you tackled from the safety of your Awesome Personnel Carrier in the first game.
1) The thresher maw. This is a giant worm thing that shoots poison that can kill you in two hits and can only be hit at range.
2) The Geth Colossus. Not so bad in the first game when you could drive circles around it while whittling its shields down with your vehicle-mounted cannon. Here, you're fighting it on foot with small arms, and it has cover and infantry support. On Hardcore or Insanity (which you have to do in order to get the Bonus Weapon), the thing fires its pulses really fast to keep you in cover while its buddies run around and kill you.
Tela Vasir in the Lair of the Shadow Broker DLC definitely fits here. She's easily one of the toughest bosses in the series. She has extremely high barrier and armor defenses. She's ridiculously accurate with her battle rifle, uses a biotic charge (something that only Vanguard Shepard was capable of before), shockwave, and tech armor.
An optional Mass Effect 2 That One Boss features in the Kasumi's Stolen Memory DLC in the form of Donovan Hock at the end of her loyalty mission. At first it seems like a standard gunship battle, of which there are two in the main game. This one is different however, in that squadrons of Eclipse mercenaries and LOKI mechs will continually spawn that you have to take care of while Hock pelts you with fire from his gunship. Oh, and when you deplete the ship's shields, they simply regenerate to full. Also, the way the cover on the platform where you fight Hock means that there's a good chance he'll be able to fire at you from behind or the side while you're taking cover from the Eclipse mercs swarming the platform. Adding to this, your party for the Hock fight consists only of Shepard and Kasumi, since you can't take a third partymember to Bekenstein. It becomes pathetically easy after Kasumi uses some fancy acrobatics to permanently disable the gunship's shields, but to get to that point you have to survive several large waves of Eclipse mercs.
Enyala, the boss of Miranda's loyalty mission. A relatively unimportant enemy who ends up being a nightmare, especially on higher difficulties. She fights with the rare and devastating Claymore shotgun and powerful biotic attacks, and has multiple layers of protection, as well as a large number of Elite Mooks backing her up. What really makes her boss fight into a controller-thrower, though, is the layout of the area you fight her in. It's set up like the perimeter of a rectangle, with a walled pit in the center. She comes around one side, while her troops take the other, trying to catch you in a pincer. While Mass Effect 2 usually gives you a good length of time to recover health and shields between volleys, this battle comes with a pretty strict time limit, because if you delay even a little, she and her mooks will surround your squad and make you die. Both she and her mooks are immune to crowd control abilities until their protection is stripped (and being elites, the mooks have protection even on lower difficulty levels), and there's a very good chance your squadmates will get taken out by her allies before you can finish her off, or vice versa.
The bosses of Jack's and Grunt's recruitment missions also deserve mention. In Jack's, Warden Kuril has taken up residence behind a shield that has to have its emitters - which are spread out across the field - taken out, in a horrible snarled mess of a battlefield with awkwardly positioned waist-height walls and well-defended enemies who can come from virtually anywhere. In Grunt's, you need to deal with an YMIR mech, Jedore herself, and a seemingly endless chain of berserk, armoured krogan (there are actually only about four of them, but it feels like dozens - especially given the krogan Healing Factor) who stroll forward firing shotguns at you and climb up onto the walkway you're on to flank you. Both of these are early enough in the game that you probably don't have high-level powers or all that many teammate options.
The Oculus. Like the Praetorian, the Oculus will float towards you. Only thing is, all the tricks you once used to defeat Praetorians no longer work. There's no other mooks in the fight to charge at (and away from the boss), it sees through Tactical Cloak, and it has a single monolithic armor bar (which is immense at that), so you can't DPS it into a recovery phase.
Mass Effect 1: The... beloved krogan battlemaster at the end of Therum. Most players go there fairly early on to get Liara. Most players have, up to this point, had a relatively easy time of it. And thus most players will die immediately. What makes it even more frustrating is that the game will not autosave immediately before the fight, so you'll end up getting reeeeal familiar with the dialogue immediately before.
Matriarch Benezia can also be tough. She can use her biotics to move your cover or cripple you, and to make matters worse, you have to deal with Asari Commandos and Geth Snipers (which can kill you in one hit, by the way).
Benezia's boss fight is made substantially more difficult, not by the enemies you face, but simply by the way it's laid out. The game saves – then there's a two-minute interchange between her and Shepard, three waves of asari and geth, another save point, another lengthy speech, and a final wave of enemies that are even deadlier than the first three. What's more, the level seems designed to make the battle as hard for you as possible, with virtually no solid/stationary cover, plenty of ways for enemies to flank you, and narrow walkways that drive your camera positioning insane whenever you're flung into their walls by Throw or Neural Shock.
Mass Effect 3 contains an unintentional example: Marauder Shields, the last Marauder you meet in the game while limping, wounded, to the Citadel transport beam in the finale. While normally a simple Mook — and this encounter was intended as such — in this section, you have only a pistol and no shields, so on Insanity difficulty, he may well become the toughest encounter in the game, killing you if you miss even once. The Extended Cut significantly nerfs Marauder Shields's, well, shields, making the fight much easier.
Labyrinth of Touhou has plenty of these:
Youmu Konpaku, who is almost guaranteed to give you hell. For starters, she's teamed up with her ghost half who rains down status effects on your party, while she devastates your whole team with her absurdly powerful sword attacks. Thankfully, the ghost goes down fairly easily. Youmu, on the other hand, has a whopping 24,000 hp, with the most you're capable of doing at best is 1000 or so. And about half the characters at your disposal are weak to physical attacks, the only moves Youmu uses, and die to them instantly.
Judging by the above, you'd probably think that it's a good idea to focus on the ghost, considering that it has less health. You'd be very, very wrong. Upon it going down, Youmu goes completely insane with her attacks, using her elemental attacks more often and also beginning to use Slash of Eternity, which is ungodly powerful.
The Eientei trio, against whom you must kill Eirin and Kaguya at the same time or else face an instant game-over from either Astronomical Entombing or Danmaku Barrage.
Luckily, characters high Spirit Affinity can resist them somewhat, so equipping characters like Komachi with the +128 SPI affinity item helps a lot
Yuyuko, a.k.a. "Whoops, here's a multi-target attack with 200% chance of instant death."
Flandre, whose Levatein obliterates anyone not with tankish stats and about 500 FIR affinity.
Yukari, who uses Djinn "I totally cribbed this from Golden Sun" Storm to drain all SP from ALL your characters (including those in reserve). And she'll always use it in battle twice, including once just before her Turns Red phase.
Hibachi #1 and 2, who are like Eirin and Kaguya, only even more unforgiving, and with relatively infinite DEF or MND.
Utsuho, who busts out Giga Flare from out of nowhere without any warning at all. If you're not expecting Mystic attacks on a Fire-based boss, then you are screwed.
Chen, of all people, can be absolutely devastating. Thanks to the area you fight her in being full of powerful magic energy, her speed is through the roof, allowing her to attack pretty much every second. And her main attack is an incredibly powerful physical attacks, at a point where over half your party consists of Squishy Wizards. Oh, and did I mention she's the first story boss of the game?
In Aion, Draupnir Cave is supposed to be, progression-wise, the fourth-hardest dungeon in game (third-hardest for either faction, since two of the following dungeons are restricted by faction). The last boss of Draupnir Cave is harder than anything in the later dungeons except perhaps the hardest of the bonus bosses in the final dungeon. In earlier versions of the game, the captain of the pirate ship Steel Rake was also That One Boss, until his Nerf.
The MMORPG Vanguard: Saga of Heroes has many very hard bosses, but most importantly Akande, which is necessary to kill to get the Griffon, the standard flying mount of the game. This boss was nigh impossible for anyone but best equipped groups, which still kept failing a lot. There was supposed to be a trick to kill Akande easily, but apparently nobody ever found out what it was. Even after Akande was toned down a lot later, it was still an almost impossible kill.
Action RPGMetal Walker has one in the form of B. Dragon. He does a fair amount of damage even if you grinded...and his amount of HP is MASSIVE. Even if you do 77 damage with each hit, he will likely kill you before you kill him, especially if he or his minions get good capsules.
The level in GPG's RPG Space Siege where you decline Jake's offer of joining the Dark Side has you fighting a unfair number of fights, but the piss taker is Jake himself. His Railgun attack is easy to avoid, but if it hits you it takes off a fifth of your Health Bar, but the real dick move is the undogable Fire Trap Spam (for want of better term) that turns a third of the playing field into mines. Which you can't destroy with the rocket launcher, but you can trick into detonating with HR-V or yourself. Think you can keep doing that in a game with sticky controls?
The 3 Death Knights in Mystic Ark is hands down, one of the hardest boss fights in the game. They all can attack for massive amounts of damage, Lux and Reeshine being the only ones who can take a hit rather well, they also know a moderately powerful fire spell, and all know the Kill spell to top it off. Unlike in The 7th Saga though, getting a party member, especially the main hero killed is sort of a big deal. To make matters worse, one of them will start casting the second best healing spell in the game if its allies are being threatened. Fortunately, the Deathguard spell/the Cross item helps take care of the Kill problem. Too bad they can still team up and annihilate, if they wanted to or if you're just plain unlucky, the main character, who is a Glass Cannon, the White Mage, and/or the Squishy Wizard.
The "Beast" is also a royal pain, being a Duel Boss in a game where the hero has only slightly more defensive capabilities than the squishy wizards. The thing hits hard, too.
In Sonic Chronicles: The Dark Brotherhood, there are two actual boss fights that are absolutely enraging. The first is against the TWIN giant scorpions, and the second is the fight with the TWIN Swat Bot MKIIs. The Giant Scorpions are hard the first run through the game for many reasons. They can easily poison you, they have very powerful attacks, they have way more health than ANYTHING you've seen thus far, and most importantly, your characters have virtually no upgrades on their specials. The Swat Bots, on the other hand, have downright ridiculous health, insane defense, and the ability to resurrect themselves. If you don't kill BOTH on the same round, they'll get back up with 50 health. On your first run, you're hitting for maybe 15 damage if you're lucky at this point. The only consolation you get is that it is VERY EASY to prevent their specials from hitting you.
Monster Racers has Reinhart. After a Hopeless Boss Fight very early on (which will cause him to go nuts if you manage to beat him and his then-level-35 monster - for reference, you're expected to be at level 8), most players would've eventually settled into the groove of 2 high bells and a ring of knowledge for everything except tournaments, where they would shuffle their equipment around to give their monsters an edge in the races. This works fine and dandy up until the European GP, where being 20 levels above EVERYONE BUT REINHART (and having fed your monster of choice lots of candy) will still make the difference in time between you and Reinhart's beast of a monster less than half a second. Making this much more painful is when he tells you immediately afterward that he was only beaten by one other racer.
The boss preceding Reinhart, Santos, isn't that easy either. Like the Reinhart example right above, this boss has a large speed boost on the terrain that his stage uses a lot. To make things worse, he has great speed and acceleration, and a defensive skill that means just bashing into him won't do you any good.
Even worse, there is a late-game battle that features you against Reinhart and Santos at the same time. And a third boss, just to add insult to injury.
Terranigma's Bloody Mary is the combo breaker in a series of reasonably easy minor bosses. She has high defense and powerful attacks, plus a floating ring of masks or something that screw you every time, as Ark's physical attacks are all close range. Your best bet is a magic ring, and you're limited to 9 of those.
RuneScape gives us Nomad, generally agreed to be one of the hardest fights in the game. The highest amount of health you can have is 990. He has 20000, and his normal attack can hit in the middle 300s. He has quite a few special attacks, but two stand out. The first must has to be ran from, or you get hit with 750 damage. The other sees you teleported in front of him, and frozen, meaning you can only stand there and cram food into your mouth as he charges up a vicious HP to One attack. It does your maximum health minus one. So if you have a max of 990, it does 989. You didn't have full health? "Oh dear, you're dead."
With the release of Dominion Tower, there is a challenge that you will have to fight him twice in a row without using the bank or taking a break. Good luck!
Although he was made much easier after the release of ganodermic armour.
Iand designed by players at Runefest, Sunfreet has appeared at the Dominion Tower. Statistically he's weaker than Nomad, however his match prohibits prayer, power-ups, special attacks, or familiars from being used. Not only that but he hits hard, his specials hit hard and has incredible defence.
Vanstrom Klause isn't quite Nomad-caliber, but he's still pretty damn aggravating. His normal attacks hit quite hard and can even hit through prayer, although praying will take the edge off. He also has a bevy of special attacks. While most of these are nasty if you don't know how to avoid them, his darkness attack stands out. He yells 'Stare into the darkness!' and you are told to look away from him to avoid being damaged. You'd think this means 'position your character facing away from him' but it actually means you're supposed to angle the camera away from him. Not knowing how to reliably dodge this attack makes the fight almost impossible to beat.
Yk'Lagor the Thunderous was this with his one-hitting earthquake attack before the players figured something out.
Runebound Behemoth. Especially if you are not familiar. He uses all three protection prayers at once, making him invulnerable. You could only disable them one by one but they go back up in a few seconds. Did we mention he has a special attack that hits everyone by almost as much as the max health?
Shadow-forger Ihlakhizan. Hits up to over 80% of maximum health with his special attack, which also drains all your stats to half. Even if you tanked it, you probably won't stand a chance after that.
This is devastating to freeplayers, who have no method of recovering lost stats. Members can at least make a potion to recover.
Blink. In order to damage him, you have to raise a pillar in the room for him to run into. Only one pillar can be raised at a time, and it must be raised well before he gets to it. Sounds annoying, but not hard, right? Did I mention that while running, whenever he runs past you, even if you are standing far away, you will frequently get slammed with a massive chunk of damage out of nowhere?
Tok Haar Hok from the Elder Kiln was a big one. Hok is essentially a lava monster who acts as a prophet for an Elder God of fire, and he lives up to that big time. Hok himself isn't terribly tough, but once his health hits halfway, he'll try to heal. To prevent this, you must stun him before he steps into the lava waterfall. Easy enough. Did I mention that this is in a tiny arena, he spawns heavy hitting minions, and the floor of the arena also erupts lava from time to time, forcing you to be on the move? To make matters worse, The Elder Kiln quest was the first major combat quest released after the overhaul to combat, so many players had not yet mastered the new system.
Hreidmar from the dwarf quest series. The minions by themselves aren't too bad, until Hreidmar has them suicide bomb you, uses a spell that makes them inflict heavy damage on you, or heals. When he prepares to heal, you must damage him with an ultimate ability, or he will regain a huge chunk of health. If your ultimate attack fails, and it often does, you will not be able to recharge in time.
Enakhra from the World Wakes. Once you figure out how to stop her healing ability she's not too bad. If you don't, though, she'll siphon your health by a certain percentage. Many players tried to stop this by staying at low health, which is an obvious disadvantage. She'll also occasionally teleport on top of you, hold you to the ground, and stun you.
In the first Dark Cloud game, there is one boss that will absolutely mop the floor with you over and over and over and over and over... Anyone who has played the game can tell you: Ice Queen La Saia is EVIL. First, you have to kill the magic-resistant shield she is using. Alright, you've got 3 characters who aren't magic users, so it shouldn't be that hard, right? ABSOLUTELY WRONG. For she has several varieties of projectiles, one of which FREEZES YOU IN PLACE, and one which drops a gigantic block of ice For Massive Damage. Which she will use in combination. And she'll distance herself from you CONSTANTLY. Alright, so you take out the shield, now what? Good luck damaging her, as without using Fire element with a pretty high score on your weapon, you will do all of shit to her. And only the sole Magic user on the team can damage her without using items. La Saia is still capable of freezing you and hurting you QUITE badly. If the magic user dies, and you lack revival powder, guess what? You lose. Right there. And she has FAR more health than the two bosses that precede her (though Dran takes an insane amount of hits to take out if you haven't been using Xiao a lot). Oh and the BGM doesn't help. AT ALL.
Neoquest and Neoquest II, the RPG games on the Neopets website have a few examples. In Neoquest I, Archmagus of Roo can cause players within his level range a lot of pain and suffering, and the Final Boss is very difficult as well. In Neoquest II, Zombom, an early boss in the game can do a lot of damage with his Decimate spell for that point in the game, and you only have one party character to fight with. The Leximp can also cause players a lot of problems as well. The Four Faeries, Hubrid Nox, and King Terask are the hardest bosses in the game, hitting extremely hard and are capable of healing.
MagicMan.EXE in the first Mega Man Battle Network. His own attack blocks one row of your field, and then he summons two Mooks who might just Deadlock you.
BubbleMan.EXE in Battle Network 3. ENDLESS RESPAWNING BUBBLES ATTACK FROM HOLES IN FLOOR, YES, THANK YOU. Also he envelops himself in a bubble shield, and the player has to destroy that before being able to damage him, which takes a hard hitting attack, but you can't really use a chip card because that'd be depleting your deck and just arghwhattasflkdjI want toasfdmachen wis das TOT GEHEN.
It gets worse when fighting his v3 form, since the only way he'll even show up is if your HP is critical. That's just plain mean.
CloudMan.EXE in Battle Network 5 is almost as bad as BubbleMan. He hangs out in the back column with clouds protecting him, while periodically summoning one in your field that shoots electricity. Using a Navi-summoning chip to break through his defenses for a free hit? The clouds absorb all the damage, meaning the only feasible way to take them out is with buster shots...but that doesn't stop Cloud from summoning more. Then there's that damn moving thundercloud pillar with Cloud hiding inside one of his panels... Granted, if you have a Lance, you can push him out of the back column and do a huge amount of damage right off the bat. If not, good luck. And unlike Bubble, it is mandatory to fight all three of his forms if you want to complete the postgame.
The Ravager in Jade Empire hits hard, can recover his health in seconds with Chi healing, and is fond of rolling away or using area attacks to prevent the player from killing him before he can recover. He also has unlimited Chi, which makes it a matter of killing him before he can regenerate.
The Dirge Clones on Jade Master difficulty are incredibly hard to beat, since none of the cheesy strategies that you need to stand a chance against the bosses are particularly useful in this fight. Unless you exploit the poor pathfinding AI, it seems almost impossible to win, and even then it's a handful.
Goresby Purrvis, The Dragon of Dragon Quest IX, is widely considered to be one of the hardest bosses in the game barring the final boss and the grotto bosses. For one, he is insanely fast, is similarly extremely powerful, and is fond of using an upwards thrust attack that will, 100% of the time, knock the target down, rendering him/her inactive for a turn. Oh, and he can also use Hatchet Man, which he makes liberal use of throughout the fight.
Baron Brixius in the flash game Sonny 2. He has an utterly absurd HP total, upwards of 48,000 (to put that into perspective, you fight Brixius in the middle of the second area, and the game's Final Boss in the fifth area has slightly over 14,000.) He also loves casting one of the nastiest debuffs the game has to offer - a very powerful poison that will kill any character in 10 turns if you don't heal them, and that's assuming they're at full health when it hits them AND that Brixius doesn't simply attack them to make it even faster. AND this poison also reduces any healing the afflicted character receives by half. It's also impossible to cure, except by waiting for it to wear off - in 10 turns. So you have to spend the vast majority of what would have already been a very long battle healing, because you need all the help you can get, and there is no way to revive dead characters mid-battle in this game. Oh, and it's not like there's anything stopping Brixius from casting his poison spell on multiple characters at once. This is all on the game's easy mode.
Brixius might count more as a Puzzle Boss however - The actual trick to him is to keep draining his focus (the game's equivalent of MP), which will make him apply a buff that restores it that also damages him. All 3 classes have access to at least one focus draining ability.
There is also the Hydra, the final boss of the 4th area - Just like Brixius, there have been multiple threads on sites where the game is hosted asking how to kill it.
Golden Sun has the Kraken, boss of a sailing ship on the Karagol Sea. He's got 2400 HP, quite a bit more than the last boss's 1700 HP, and like most bosses in the game gets two attacks per turn. Even worse, it knows Ply, which heals it for about 100 HP a pop. Also, almost all of its attacks have a high chance of either inflicting status (such as its favorites Dark Blessing, Water Blessing. and Poison Beat) or of ignoring stats (Such as Spinning Beat, which has a chance of treating someone's defense as though it were HALVED). Add on a minuscule chance of it pulling a nastily powerful mercury elemental attack and you're pretty screwed over. No wonder most people who run from a few fights get stuck here, especially since once you get on the Karagol sea you can't go back to grind levels or buy new equipment and items.
Coming after Lamakan Desert, the Manticore can be a difficult boss. Unless you were really diligent with the oasis searching, you might be weakened from sunstroke. In addition, the Manticore can move twice per turn, and is the first boss to do so, so it will catch a new player off guard.
Orb Of Undead from Baldur’s Gate: Dark Alliance, he's not particularly hard on single player, but on co-op he get's buffed considerably, The Orb Of Undead is a Flunky Boss who summons an army of undead to fight the player, when he summons his army he flies out of reach, and will only come down once you have killed all of his minions, but when he comes down he only he comes down for a few seconds before repeating the process, there's enough skeletons to surrond the player, and they can do it quickly doing high damage, don't be fooled, these skeletons aren't really cannon fodder you can kill in just a couple of hits.
Flame Lurker is highly agile, highly aggressive, leaves few openings where it is truly safe to attack, and is a melee boss with various attacks that cover a wide range. To make matters worse, when it loses between half to three-quarters of its health it goes berserk and has pretty much all its attacks do radius damage. Flame resistance helps a lot, but even then it can cut down all but the toughest tanks (who can at least rely on high stamina along with a good shield) in a couple of direct hits, and gives few opportunities to heal.
Maneater is also very aggressive and fast, and in particular it has an incredibly annoying pounce attack that does heavy damage and can easily knock you off the thin ledge the majority of the arena is made up of (thankfully the centre of the arena is mostly safe from this problem, except you have to move past it to get there). Oh yeah, and there are two who are both equally dangerous, although it is possible to wipe out the first one before the second becomes an issue. As a bonus, its understated introduction of demonic eyes approaching from the darkness is Nightmare Fuel.
False King is another Lightning Bruiser type boss (notice a pattern?), who can unleash many quick combos and easily break the guard of all but the toughest fighters. He also has an instant kill attack that covers at least a third of the arena (although you can knock him out of it pretty easily), and is the only (computer controlled) enemy in the game with an attack that can Level Drain you.
There's an easy way to determine if a person has played Agarest Senki through the midway point. Mention the words Midas and Phoenix Wave in the same sentence, and see if the person you are talking to starts frothing in rage. Of course, there's also the massive amount of HP, the 12% HP regen that is difficult to break without certainattacks, and the other myriad of overkill attacks he can use that are normally left as combination specials. God help you if you haven't obtained one or more useful EX 2 combinations, Execution, Gore Crush, and don't want to do the extra Level Grinding to promotion level.
Many of the end-level bosses in the PC game for Lord of the Rings: Return of the King had various tricks and unusual ways you had to fight them, but most were fairly straightforward- There were patterns to their summoned allies, points where they couldn't be attacked, and times they were vulnerable. Then there was Gorbag, at the end of the "Minas Morgul" level. The only way to beat him was to first break his shield- which required a spear- then immobilize him- which required another spear- and only then would his health bar appear so you could wail on him for a few seconds before he got another shield. And actually picking up these spears, since you're a freaking Hobbit, takes forever, during which you're vulnerable to attack (Which knocks the spear out of your hand, so you have to get another one.) Oh, and he'll also leap at you across the whole level and begin rapidly assaulting you if you stay in one place (ie near the spears) for too long. Oh, and after you break the shield, he'll still fight, still be immune, and keep trying to attack you until you get that second spear. And don't take too long with that second spear, or he'll just grab another shield and you have to START ALL OVER AGAIN.
Ys IV(the PC Engine version) has its Big Bad Arem, possibly the hardest final boss outside the remakes. He has three life bars, Turns Red for his second, can regenerate his HP, it takes an extremely long time to whittle down his HP even if your EXP is maxed out, and bombards you with a shitload of hard-to-avoid highly damaging attacks.
Agarest Senki 2 may not be crossing the Nintendo Hard line, but that doesn't mean that this game doesn't have the resident That One Boss. Pain, thy name is Sophia, one of your party members. She herself as a boss really isn't hard at all. What makes her hard is if you did not have any back up party members due to the fact that at this point, you lose four of your party members due to a series of PlayerPunches. Oh, and this is also a case of Boss Rush due to the fact that before you even fight her, you are fighting off against two bosses who aren't hard themselves. However, whatever HP you have left at your last fight, it still carries over to this fight. And woe befall to you if you didn't equip your reserves with any equipment due to the fact that the game will not allow you to change equipment while in this section.
In the flash game Book of Mages: The Dark Times, we have Witchthorn. He is one of a very small number of opponents who will use Cursed bolts, which reduce your character's strength, and can stack to the point where your strength falls all the way to 1. The problem is that Witchthorn has 610 HP, in a game where 300 HP is above average and endgame-level enemies typically have somewhere from 300 to 400; never mind that you typically fight Witchthorn in the midgame, making for an absurd Marathon Boss. While the bolts can normally be blocked, Witchthorn will usually cast Silence before you have a chance to kill him, and when he does this, you are about to get cursed and there is absolutely nothing you can do about it. To cap it all, if you choose to spare his life after your first fight, you might have to face him again.
Burnstorm also counts, mostly for his Combined bolt. This attack does an amount of damage exponentially above what Combined bolts are normally capable of; it's virtually guaranteed to one-hit kill you. And once his Special bar gets high enough, he will do nothing but spam that attack for the rest of the fight; note that another one of his abilities increases his Special bar. If you fail to prevent him from firing this attack, even once, you lose. To make matters worse, he is one of a vanishingly small number of opponents who can dispel status effects; good luck if you're playing a clan that relies on those, such as Dark Wood, which is otherwise the best clan to beat the game with, or Poison Water, with its complete reliance on the Poison effect.
Another obnoxious opponent is Chilldream, who stands out as the only opponent in the game who isn't a Bonus Boss but can do something your character can never do - shooting 20 high attack bolts at once (your max is 15). Since Chilldream has maxed out attack power, that means 50 unblockable damage per round unless you got the High Defend Bonus skill (which is mutually exclusive with Low Attack Bonus, the latter of which is much more useful in literally every battle except this one). This assumes he doesn't simply cast Freeze Defend, which deals 100 unblockable damage. This, in a game where you might have 400 HP in time for the final boss, and are likely to have under 200 around the time you can first face Chilldream. The saving grace is that it's possible to avoid facing him with clever use of the game's Relationship system, though doing this causes you to gain Reputation points (when on the Black path you want as few of these as possible, and Black players are the only ones who have to face Chilldream in the first place.)
Champions Online rarely has such bosses, mostly because all of the most powerful ones are pretty much for a full party (meaning at least SOMEONE has the right powers to either keep him busy or take him down), or a full open environment beatdown by everyone who can gather there, or have a specific method and set of tactics for defeating them that most players can do solo (though not without taking a world of hurt in some cases). However, in the Demonflame adventure pack, the final boss BECOMES That One Boss not because of him - but because of the horrible AI of your mandatory assistant. You must keep the Boss and his summoned mook busy as your assistant opens five mystic chests, releasing the power contained within. Unfortunately, it is timed - and if the Boss or his mook attacks the assistant, the assistant fights back - and keeps fighting until his target is dead, even if he's not being attacked anymore. Solo attempts on this boss are possible - but if you lose twice, you're given a "mercy" win with no rewards and you'd have to start the whole adventure pack over again to try for a 'solid' win once more.
Return To Krondor has a few bosses that are candidates for this trope. The first candidate is a demon. This demon is huge, red, and muscular. It does not use magic attacks, but it has a claw attack that will hit your characters very hard and almost never misses. It is pretty much immune to magic attacks (However, it is possible to blind this monster with the spell Behold the Birthing Sun - the second last magic spell you can unlock in the Fire Spells section). This demon a lot of health points, and you will need a good sword to hurt it. Your party against this demon consists of James the thief and Jazhara the mage. Wait, that's not all! Your decisions in the game will cause one out of a few scenarios to occur: 1. You fight the demon and one necromancer in a small room, 2. You fight the demon and two mages in a small room, or 3. You fight the demon, one necromancer, and at least four Nighthawks in the Bar. Have fun! The second candidate is at least one of the Grey Talon Mercernaries. Some of them have magical armour and weapons. This means that if you did not properly prepare for this fight, then you are going to spend forever trying to inflict damage on them. The party consists of William the warrior and six Krondorian guards. The third candidate is the Vampire Lord. Your decisions will result in one or two fights with this boss. One of the fights has the boss being able to completely restore all his health (He has a lot of health points) every time you bring it down to zero. He also will very likely hit you, and not only does he hit hard, but the vampire bite adds a lot to the damage he inflicts. This means that he can topple mighty Solon in a few hits. That fight ends after a number of turns, in which the Vampire Lord disappears in a puff of smoke. The other fight with him is the same as the last one with two differences: 1. He can no longer completely restore his health when you bring it down to zero and 2. He has three vampires and a zombie backing him up. At least this time he dies for good after a number of turns...if you last that long. The party consists of James the thief, Jazhara the mage, Kendaric the mage, and Solon the warrior-priest. The fourth candidate is the Dragon Soul. This boss is practically immune to attacks except for magic swords. It will simply shoot chain lightning at you on every turn. There is little defense against magic attacks. All you can do is try to survive for enough turns before it is automatically defeated. The party is the same as the one fighting the Vampire Lord.
Not only is Chaos Lord Ledgermayne in AdventureQuest Worlds bent on starving off all of Lore by sealing off ALL magic from it, it is also so incredibly tough to beat that it'll probably give you nightmares every time you fight it, especially if you're at a low level. Its toughness is explained by the special boss mechanic worked into it that requires you to pay attention during the fight. Every one in a while, it will automatically warp to the center of the battlefield and give off a colorful glow and a message will pop up, warning, "Ledgermayne charges a powerful attack! Enter the glowing safe zone!" This message urges you to quickly run to the glowing safe zones that open up every time it does this, and if you're not there in time, then the resulting blast from the attack will hit you with MASSIVE DAMAGE and, if you have under 1,200-1,600 HP, it can easily KILL YOU. Of course, once you're in the safe zones, the blast will end up healing you.
Wolfwing, an earlier Chaos Lord, can be a pain as well. Whenever you fight him, every time you've taken enough HP off of him, he will use an attack that hits one player for huge damage and, worse yet, heals him. He'll do this about five times per fight, and once his HP hits below 10,000 or a little lower, a message will pop up saying "Wolfwing goes berserk! End this before he ends you!" and therefore he'll start attacking TWICE AS FAST! He can heal himself at least two more times when he's berserk, too. Whoa.
Ladies and gentlemen, meet Tibicenas, the eighth Lord of Chaos. Just like Wolfwing, Tibi will steal HP from as many targeted players as he wants every time enough HP is taken off him. He'll do this about eight times per fight, and by the time he steals HP for the sixth time once his HP hits below 5,500, that's when he goes berserk, as evidenced by attacking twice as fast as a message pops up saying "Tibicenas goes berserk! Kill him quickly!" If you're unlucky, his HP-stealing AoE can even leave you with just 1 HP, no matter how much HP you have left.
And then there's his revenge-shade, Ultra-Tibicenas. He has almost the same amount of HP as the Frost King, plus, he steals HP more often and can even use an attack that petrifies at least one player for a few seconds every once in a while. Worst of all, he WILL go berserk once his HP hits below 20,000, therefore he'll start attacking twice as fast by the time a message pops up saying "Ultra-Tibicenas goes berserk! Kill him quickly!" Now this guy feels like he seems hopeless to defeat.
The third Chaos Lord, namely Vath, also counts as That One Boss. Basically, he has Stalagbite, and both have low HP, but here's the catch - if you attack Stalagbite first, your damage will be significantly reduced when attacking Vath. And if you attack Vath first (or have someone in the zone attack him while you're going after Stalagbite)? Stalagbite will gain an enormous boost to his attack power and do quad-digit damage, usually resulting in a Total Party Kill.
The Final Boss of Phantasy Star Portable 2 Infinity, yet another Dark Force/Falz/Fulkis, is pretty ridiculous. Its level scales to anywhere between 25 to 88, meaning that unless you fight it past level 100, you're going to be subject to the following: defense so ridiculously high you'll be surprised to ever see anything past 15, a size so cosmically out of scale that you can't even fit anything past its heels on the screen, trampling damage like most any other walking boss (De Ragan, etc.), most attack will easily take out half your HP, some attacks which can chain you to death if you're too stupid to keep strafing, and that's before it Turns Red. When it gets to low HP (of course there's no way to see how much it has; that would give you hope), the game's theme starts playing (which may or may not be an Ear Worm or Hell Is That Noise depending on the person) and it start attacking twice as fast and with extended combos. Then it disappears, and unless you've got a lot of HP, a good block ready, or great reflexes to dodge, will reappear right over you and do what for most will be an One-Hit Kill attack. The fight can easily last for over 20 minutes, in which you'll run dry of all your monomates, dimates, trimates, star atomizers, and any and all PP on Resta. Didn't bring a good light weapon or strong dark armor? You're dead.
The first battle with Ichii in the Pokémon EmeraldGame ModTouhoumon World Link is a prime example of a brutal Wake-Up Call Boss. It might not seem so bad at a glance; she only has one Boneka, Rin, and she's at Level 3. The problem? It's moves. WHY THE HELL DOES A LEVEL 3 BONEKA KNOW THUNDERSHOCK AND HYPER VOICE?! And Rin has a lot more HP than anything else at her level, as well as a Sitrus Berry to bring its health back up once you start doing damage to it. Ichii will also start the fight by using an X Special, making ThunderShock hurt more. Picking Kurumi as your starter makes this fight a little easier, as Pursuit does more damage with her, and she also has Synchronize to inflict Paralysis on Rin, thereby forcing Ichii to waste her turn by using a non-working Energy Root and lowering Rin's speed. If you picked anybody else? Good luck.
Most of the Gym Leaders tend to be this on some level. Roxanne with her underleveled Tenshi's Hisou Sword (Which amounts to a Ground type Hyper Beam in the FIRST GYM), Wattson with his underleveled E Chiyuri (at Level 26, which is higher than the rest of his Boneka and all of the Pokemon around the area), and Tate and Liza's entire team unless you know a specific strategy to defeat them.
In Mega Man Star Force 3, two storyline bosses really stand out; Acid Ace and Dread Joker. Ace has a large pool of attacks and never follows any clear pattern with his attacks. Joker has Super Armor, meaning he doesn't flinch. On top of this, he has a laser attack that takes up the whole screen, so the only way to not take damage is to time your attacks so that he's knocked out of it. Much later in the game, you fight upgraded versions of both of them back-to-back.
The fight with the Soldum Telethia ranks as (one of) the hardest in Xenoblade for many players. It's not really the Boss himself that's the problem: it's Tyrea who fights alongside him. The Telethia will evade any and all attacks unless you use Purge on it. easy enough. But you've only got so much time before the effects of Purge wear off and it begins attacking again. This is annoying but not impossible. Tyrea makes it worse because not only is she capable of attacking any of your characters, she's also capable of casting a Shield on the Telethia, making damaging him very difficult indeed. Now you may think it's easy to get around this, just take Tyrea out first right? WRONG! The Telethia likes to use a move that's kinda like Pokemon's Follow Me, as it forces you to attack the Telethia himself. Oh, and if you're using Shulk, which you probably are since only him can silence the Telethia, all his attacks will do Scratch Damage to Tyrea. Fun times.
The second fight with Jade Face is a strong contender as well (The first one is simply a Trick Boss and he runs away after you deal some damage). Not only he keeps summoning mooks to annoy you, he's got several powerful attacks (Especially Laser Bullet) which unless you tank will decimate your party, and he's fairly durable, even. To make matters worse, the game makes you think you might auto-win after dealing a set ammount of his HP on damage since you're "buying time"... nope, you do have to deplete all his HP. To put in perspective, you face HIS boss five minutes later, and despite him having similar tactics, he's much easier.
Rune Factory 3: Even among the jacked-up bosses within the Sharance Maze, Golem and Siren stand out. Most have near-full-screen, multi-hit magic attacks which, while powerful, can be nerfed or outright nullified with the right equipment (Or dodged with the Rocket Shoes). Except for the Golem - which simply chases you around with multi-hit punch attacks and Rocket Punches and dizzies you with nearly every blow (setting you up for a knockout follow-up) and Siren - which has "Siren Song". It throws musical notes at you, each color does different elemental damage (did we mention the accessories that nullify damage from one element gives you double damage from it's opposite?). It also contains black notes that will One-Hit KO you. Oh, and as the notes drift towards you, they change color. So that water note drifting towards you could suddenly become fire or death just before it it hits you. Like many bosses on this list, if you have the right equipment, they're nothing to worry about. If you don't, you die.
DC Universe Online: Go into the general chat, mention PengiBot Maximus or the Penguin himself, and witness many highly equipped players swear like sailors. The former has dash and spin attacks that can suck you in and kill you in seconds, plus adds that can freeze or you set you on fire, blow you up or heal him making it hard to keep your distance and not get hit...and he's just the MINI-BOSS in the instance. The latter has an umbrella with a stun for close range, a machine gun or flamethrower for mid range and a grenade launcher that can hit you anywhere in the room all of the above will melt your face off in seconds. Even better? Its a SOLO mission so you can't bring pals to share the pain. They did add it as a Duo mission and dropped the Bot from that version but still. Ow.
Aragog from the Game Boy Color version of Harry Potter and the Chamber of Secrets. His attacks take roughly 25% of your hp every turn, plus he can poison you for even more damage. Did I mention that he can paralyze you to prevent you from healing between turns? Best part is, he starts off with a surprise attack.
Breath of Fire IV has the dice known as I and II, encountered in Fou-lu's tomb. They're both packing plenty of HP - that's brutal enough. To add insult to injury, their first move is always to use Statis, which prevents you from using the game's most damaging combos. So when you decide to fall back on Ryu's HP-granting dragon forms, they bust out a move called Revolution, which randomizes your characters' HP counts (healing Ryu in dragon form is impossible without a very special, very rare item). Their regular physical attack is very brutal. But, after all is said and done, the worst part about it all is that one die will always attack before your characters and one die will always attack after your characters, meaning planning any sort of defense or healing takes some good luck.
And before you venture into the tomb, you get to fight Won-qu. Won-qu has 32,000 HP, which is about twice as much as you've seen on any boss up to this point. His physical attack is brutal; his defense is very, very good. But what makes Won-qu so frustrating is that his first move is always Frost Breath, which is very bad for two reasons - first, Ryu has a natural affinity to fire, which means Frost Breath hits him harder than average; second, it's entirely possible that half your party could be wearing armor that actually makes Frost Breath do more damage. Woe betide you if your front three fighters are wearing that armor.
A-tur (a Palette Swap of Won-qu), fought in Chedo, is no slouch either. While he's not as brutal at that point as Won-qu is when you fight him, he does show up at the end of a very, very long dungeon which has probably drained you of most of your energy.
Not to say that Griffon isn't a gigantic asshole either. The fight will either take forever or you will barely survive. Dark Element is also a complete ass if you don't know exactly what you're doing and don't have really, really powerful projectiles. Gaspard, in all incarnations, is also a horror if you don't have really powerful weapons. Like, used the photo album exploit level powerful weapons. Really, half the bosses in the game can be considered That One Boss to someone, but Sirus in Bunny form takes the cake for sure.
Dark Falz, the Final Boss of Phantasy Star Online: Episode 1, counts on all difficulties beside Normal. In Normal it's far from That One Boss territory. In Hard mode and up, however, it gains a 3rd form. Said form has an extremely powerful and impossible to dodge attack, an insta-kill attack (that's pretty easy to dodge, but still kills you if it hits), and the ability to take a piece of your soul to act as a voodoo doll so your attacks damage you as well. Plus, it can turn invincible and can't be hit by melee attacks (robbing Hunters of their one advantage).
Gynophobia, the second-to-last boss of Oersted's chapter in Live A Live, makes the final boss of the chapter feel like a mook. She comes with two attacks: Sweet Whisper and Enchantment. Sweet Whisper puts you to sleep and inflicts Drunk (which shuts off all but one of your attacks); Enchantment does massive amounts of damage and heals her for the damage done. Enchantment only hits at close range, but Sweet Whisper covers much of the arena - and your character's range is minimal in comparison, forcing you to fight within its hit radius. What's more, if you failed to find the hidden field of healing grass earlier in the chapter, you may well end up fighting Gynophobia without any means of healing yourself.
The Killachine and CPU Breaker may be this to those who played the original Hyperdimension Neptunia. They both hit pretty hard, spelling trouble even for Neptune in HDD, and the fact that you have to fight one after the other doesn't help at all. Arfoire in the final battle can be both That One Boss and a Marathon Boss if you recruited the other three goddesses.
The first fight against CFW Brave in Hyperdimension Neptunia mk2: You can only use Nepgear and Uni (No rear party members), Uni is painfully underleveled so you better make sure Nepgear is strong enough for Uni as-well, Brave can attack 2-5 times during his turn and do 200-500 pts of damage, that's not even mentioning his super move. Finally your health will be somewhere between 2000 and 4000 HP depending on whether you do or don't boost your HP with an ornament or weapon and how many quests you do.
Fallout: New Vegas stays away from bosses for the most part, but when you do find one, you need some serious skills. Most of them are Bonus Bosses, but the Giant Robo-Scorpion is not avoidable.
Rawr, an optional encounter in the already extremely tough Lonesome Road expansion, is probably the pinnacle. Although other named Deathclaws are almost as tough as him they usually appear in an area which allows you to get the drop on them, or to exploit the terrain, or if all else fails to run away from them. To fight Rawr you must go into a cramped cave, which then caves in and drops him in a corner, from which he will almost immediately spot you. Like all Deathclaws he laughs off most kinds of attacks, is lightning fast and even against the best armor in the game he will kill you in two hits on any difficulty above Normal. And unlike Ulysses and Lanius, he can't be reasoned with.
The Figureformer (and its allies) from Opoona. It's not just that the Figureformer has both plentiful HP and defense. It's not that it has a number of Mooks flanking it. And it's not just that some of those mooks are healers. It's that the Figureformer and its allies are all tanks being constantly healed and the battle is fought on a time limit. While the boss itself isn't likely to outright kill you, it and its cronies can stall for so darn long that the time limit alone will likely force you to lose.
Commander Goldy is no slouch either. He has fairly dangerous attacks and a decent amount of health, but what makes him so dangerous is, once again, the time limit. Due to his powerful hits, you're likely to spend as much time healing and setting up buffs (which are also timed, and wear out eventually) as you are actually attacking, and if you don't bring him down quickly enough bam! The auto-time-limit brings you down once again.
The Lord of the Rings: War in the North has several tough bosses but the one everyone seems to struggle with is Tharzog, the first boss. This is mainly due to his high attack power, huge amount of health and constantly respawning minions. If you haven't been upgrading your character properly then expect to get your ass handed to you repeatedly.
Another hard boss is Wulfrun who enjoys hiding behind a wall of fire and constantly pelts you with fireballs. He also averts the Squishy Wizard trope by possessing a lot of health and can do heavy damage in melee range. Whilst all the other bosses are fought at the end of chapters, Wulfrun attacks at the very start and can be a nasty surprise for ill-prepared players.
The Carn Dun Captain is Wulfrun cranked Up to Eleven. He constantly teleports, bombards you with fire and summons hordes of tough enemies that will kill you in seconds if you get surrounded. The only way to safely take him down is to shoot him with ranged weapons which takes forever if you don't have the right upgrades.
Contact Core and NKL-107 from the Facility and slaughterhouse dungeons, respectively, are quite tough for dungeon bosses at the point they are fought. Contact core has tracking lasers that move almost as fast as the characters, with a limited area to dodge within, while NKL-107 has shield that can kill players instantly if not removed, combined with some generally complex mechanics.
Machine Tyrant as well has attacks that track players and do a lot of damage if they hit, combined with a powerful Ao E attack that sometimes hits at the same time, and can be a challenge to unexperienced players when first encountered, due to the amount of attacks players need to keep track of.
Kurtis pulls this in Disgaea: Hour of Darkness. The stage leading up to him and his fight is about 15-20 levels higher than anything you've faced so far, easily the biggest spike in difficulty you have yet faced. Grinding on your first play-through isn't easy either, so Kurtis really steals a moment away from you and forces you to sit down and grind up.
"Mining Helgak" from Septerra Core. You meet it halfway through the game, before you get to do much Level Grinding and he is one of the strongest bosses, at least in HP. Somewhat understandable, since the game is greatly influenced by (to avoid the phrase "rips off") Chrono Trigger, and the minig helgak is modelled after Lavos, most likely from Hopeless Boss Fight in Ocean Palace.
In Robotrek, being an Enix game, has a load of these. But two that stand out in particular: Big Eye and De Rose. Just about up to the points where you fight them, they do a crap load of damage and have absurdly high defenses and are usually more a battle of attrition.
The Denpa Men series prides itself on being challenging, and the bosses reflect that. While there are many, many difficult bosses across the series, here are some of the worst:
The Ice and Aqua Golems in the first game. They have the ability to charge up, and can hit your entire party for truly brutal amounts of damage. This is especially so if your party happens to rely mostly on Red or Green Denpas. While there are abilities and items that can make your Men invincible, guess what? The skill costs a full 75 AP to use, meaning that unless you've stocked up on the rather rare Antenna Power items, you might only be able to use it twice per battle (if you're lucky). The Barrier item is also ludicrously expensive. Have fun!
The Ice Bug in the Guardian Tower. The whole tower itself is one long Marathon Level designed to whittle you down bit by bit, and the Ice Bug is a boss who's poised to take advantage of you when you're at your weakest. It can blow a dangerous breath that paralyzes your whole party, and it's one of the few enemies resistant to the typically endlessly applicable Light-type attacks. Which most of the enemies in the Tower are weak to, so you'll likely have a party full of them. And it's situated pretty far from any of the useful exit warps in the dungeon, so there's no good way to tailor your party to the boss without having to trek to it. Thanks to paralysis, you'll likely get by by the skin of your teeth when you do succeed.
The serpent lady boss in 2. Just getting to her is rough—unlike other bosses, she isn't found in a dungeon, but one of three randomly generated spots in the overworld. The only way to know which is to talk to a fairy in the center of the continent where she's found. And reaching that spot is timed. And there's no way to warp to those spots—you have to walk all the way there, fending off encounters along the way, during which your time limit is still ticking down. Once you actually reach her, she starts off with a Breath Weapon that can leave your entire party under the effects of the nefarious Fatal Poison. And that's to say nothing of when she literally turns her charm on, giving your entire party only a 50% chance of being able to actually attack her.
Porco Grosso in Ni No Kuni is no pushover, in either the PS3 or DS versions. In both versions, it has high defense, high HP, a resistance to physical attacks, and a brutal gatling gun move that will mow down your party. In the PS3 version, it's also insanely fast and darts around the battlefield faster than anything, making using magical attacks on it difficult.
The Nightmares in the PS3 versions. All of them are extremely fast attackers who love to spam battlefield-blasting effects. The thing that makes them really nasty, however, is the fact that they drop dark, "evil" Glims which harm you if you touch them.
Royal Jelly in the PS3 version is a Flunky Boss with massive amounts of HP who absolutely spams the battlefield with baby jellyfish. If you don't focus on getting rid of the jellyfish, they'll nickle and dime you to death. If you do focus on them, by the time you're done wiping them out, the boss will summon more. And if you focus on using hit-all attacks, your MP will vanish like that, leaving you with very little to heal with. Hope you stocked up on items!
Magmadame in the DS version. While her weakness to ice attacks is easy enough to exploit, she can deal massive amounts of damage to your entire party, and she keeps the pressure on. Since you fight her only just after acquiring the ability to catch Familiars, you likely won't have much to choose from when fighting her, and few of the storyline familiars can do much damage to her. You'll likely spend half your turns fighting her just trying to heal.
The original The Bindingof Isaac had Bloat as its love-to-hate boss, but the Wrath of the Lamb expansion introduces the even more painful Mask of Infamy. The first stage isn't hard - you have to destroy its heart whilst the mask itself wanders around the arena at random. Once the heart is dead, you can go after the mask. The problem is it is impervious to damage except from the back, which it never displays to you owing to the fact that if you cross its path it immediately homes in on you. It is also extremely fast and has a nasty habit of suddenly changing direction when you're trying to carefully close in on it. To add final insult to injury it is the only boss in the game which has no health meter, so you have no indication as to how close you are to defeating it. There are several pick-ups which make fighting it easier, but thanks to Binding of Isaac's nature there is no guarantee you will have them, nor indeed whether you'll have to fight the thing at all. If you don't have them, it's a teeth-grinding slog of a boss as you attempt to kite it from the sides without it zeroing in on you.