Yes, one company has enough examples for its own page. This is especially noticeable as typing 'Atlus' into the search bar actually generates this page instead of the main page at the top of the list. Now, why is it not called Atlus Hard?
Note: Final Bosses and Wake Up Call Bosses are not allowed unless they're overly difficult by their standards. Bonus Bosses are not allowed; they're optional and have no standards for difficulty. (Yes, even the Demi-Fiend.)
Gabriel. He will destroy you. He is immune to sword attacks and demon's physical attacks (and most Chaos demons are only good at physical attacks). Oh, and if you're on the chaos path, you probably got the Bullets of Darkness, which he is immune to. And since your main character can't cast spells, he can't do anything in this fight. This fight can last as long as an hour. Unless you are taking the law path (in which case he joins you - only for you to have to fuse him to make an item necessary to finish the game).
There's Kongokai, which is really early in the game and has decent enemies. Then there are 2 okay bosses, not too bad. Oh, and when you go to leave, you have to fight two enemies that can't be attacked at the same time by multi-hit attacks, one of whom will boost his physical power and do massive damage.
All of the Demon Summoner fights. They send waves of demons at you, with either 8 in each wave as one solid block of 8 or two groups of 4, and you can't talk your way out of them not only because they're required, but if they weren't, they're all unrecruitable species. Add in that each of your demons gets only 3 abilities, and you will quickly realize that your main character will spend most of these fights shelling out the macca to summon your other demons for the next round. On rare occasion, the first Yuriko fight will glitch so that after two turns of the first wave, her speech will start again and the first wave will regenerate.
Arachne. You have to go through a huge labyrith just to get to her that is overflowing with encounters (and it doesn't contain any items), and then at the end you find this. What really make her stand above almost all bosses before and after her is that you can't apparently charm her.
Shin Megami Tensei II has the fight with Satan around the end of the Chaos path, which primarily consists of "Satan pointed at [Name]! [Name] has died!". YHVH and Lucifer can also spam this attack if they so desire, but Satan seems to love using it the most.
The Matador defines the trope. He comes out of nowhere during an early portion of the game and is far more difficult than any boss you've fought before. His main ability, Red Capote, buffs his evasion to the maximum level, and he has several powerful Force attacks.
Matador is mentioned by a Manikin right before you encounter him and is right outside a city with a save point. Although this doesn't make him any easier, it makes it less frustrating.
There's also Mot. He stands out for a few reasons; first, he is one of the three bosses in the game who have a weakness, he comes very late in the game, and has basically 3 attacks. The actual reasons he is so hard are the fact that he is immune to everything except his weakness and physical attacks, and said 3 attacks: one is a powerful spell that your character can't be immune to; one is a buff that boosts the damage of magic attacks (and thus the previous one); and the last one is a skill that gives him 2 turns. For free. So far, not so bad. However, there is a chance he will use that last skill twice in a row or even more, effectively giving him the chance to wipe out your party without you being able to do anything about it (seen here). He also has a healing spell that gives him back around 50% of his health and a physical spell that hits the entire party— but at this point, mentioning them is just overkill.
At least Mot has a weakness, unlike Surt, whom you encounter earlier in the level before encountering Mot. Surt is a pain because he has no outstanding weaknessess, and has strong fire attacks. This is probably the only battle in the game where having a resistance to or absorption of fire attacks is necessary for a battle that won't overly frustrate you.
Trumpeter. How bad can it be when the boss himself explains how his attacks work and he STILL manages to be a pain in the ass? The boss basically says that every time he toots his horn (about every eight turns, according to him) either someone will be fully healed or die instantly. The death ability is completely unblockable, even if it's you and you're protected to the hilt against death. Life or death will strike the character with the least hit points. And note that the healing Holy Melody (but not the killing Evil Melody!) can hit him as well as you. As a result, it's common to find yourself down to nearly killing the boss when he revives completely, HP and MP.
Noah. He only has ONE element that can affect him (not a weakness) at a time, which he changes every turn. He can drain over 200 hp and mp from one of your party members, no questions asked. And while he only uses single-character spells for the first half, he hits the whole party for the second half.
Baal Avatar. She summons two healers, both of whom debuff you and de-debuff their party. Oh, and Bael's Bane turns one of your party members into a fly. This is incurable and renders them utterly useless.
While nowhere near as unforgiving as the previous examples, Daisojou deserves a mention here. His main attack drains both health and mana from its target, he can cast several instant death spells that hit the entire party, and he has access to his equivalent of the infamous Dragon Eye ability, which grants him extra press turns. Bonus points to mention that Daisoujou's instant death spells are the -On series (Hamaon, Mahamaon, Mudoon, Mamudoon), as in the higher ratio of death spells.
Pale Rider is by far the hardest of the Four Horsemen. His support, a pair of Loas, know Debilitate, which is the equivalent of casting Tarunda, Rakunda and Sukunda all at once, and they'll use it every turn they can. They also can petrify your characters, poison them, or put them to sleep. And they can self-destruct, which does unblockable damage to you and HEALS the Rider. As for the Rider himself, he knows Blight and Pestilence, both of which have a chance to poison your party. Pestilence also has an added side effect; if anyone is poisoned and then hit by Pestilence, they die and there's nothing you can do to stop it. And if the Loas die (which they will, even if you ignore them) he uses DRAGON EYE to replace them and then spend some more time smacking you around. And in addition to the poison + Pestilence combo, he can also use Dormina and Eternal Rest, which essentially does the same as above, but uses sleep instead of poison.
Before the Pale Rider comes the Red Rider. Even if he didn't have angels powering him up every turn, he'd still be pretty difficult. He uses spells like Bolt Storm, which hits random party members for high electric damage, Wind Cutter, which deals a tremendous amount of Force damage to one person, and Terrorblade, which does a ton of physical damage to everyone, can hit twice, and can make your party Panic, meaning your party members will randomly run from battle. You can call them back, sure, but if the Demi-Fiend is panicking, you can't. As for the angels, they can either use a One-Hit Kill that is horribly inaccurate and a waste of a turn, or Tarukaja, boosting the power of Terrorblade. And it can be used twice per turn.
Ouroboros, the final boss of the fifth block. Her first form isn't terribly hard, except for the fact that she heals about 160 damage per round, which is more damage than you can do to her unless you exploit her weakness to fire. Her attacks include Wild Thunder, a powerful group lightning spell, and Disaster Cycle, a spell that hits for moderate physical damage and inflicts random status ailments. That last one is really nasty because sometimes she gets really lucky with it and manages to either leave you with a dead weight party or petrify the main character (instant game over). Fortunately, your chances of seeing Disaster Cycle are slim. All this is just her first form, however. Her second form no longer regenerates every turn, but she now uses Disaster Cycle almost every turn, and whenever she's not using Disaster Cycle, she's using Wave of Death which hits the whole party for nearly 300+ physical damage per hit! Her liberal use of Disaster Cycle almost makes the fight a Luck-Based Mission.
Mem Aleph continues the proud tradition of the Neutral Path Final Boss being the hardest boss in the game. First of all, they hit like about a dozen cement trucks. Secondly, they can cast the strongest forms of every single elemental spell in the game, including both instant kill elements. Oh, and their signature attack? A multi-hit physical attack that does a truly obscene amount of damage. Bonus points for their second form having an attack that kills its target, always, with no way to protect against it. If said target happens to be the main character, instant Game Over. Not to mention said attack gives the HP that was taken from you to the boss, and by the way, Mem Aleph's second form actually changes Elemental Weaknesses; at least Noah gave you the courtesy of letting you know what its weakness was.
The Neutral path gives you the hard Mem Aleph as a boss, but not going on the Neutral path means you'll have to fight Commander Gore, one of the hardest bosses in the game. He has more HP than any boss in the game, with the exception of Demiurge (and yes, that includes the aforementioned Mem Aleph), and it's made even worse by the fact that when his HP hit 0 he heals himself for 7,500 health (his maximum is 15,000). He also hits like a damn tank, doing obscene amounts of physical and gun damage and the occasional status effects. And he has moves that give him even more power. He has the dreaded Charge/Adaptation combo which does enough damage to kill anyone who isn't defending and resistant to physical damage. And he will only use this on the main character! His absurd HP alone makes this one huge endurance test that is impossible to clear without enough Chakra Drops. Did we mention he reflects any and all physical and gun attacks?
Picked the Law ending? Then you get to fight both Gore AND Mem Aleph, on top of all the other bosses you fight in the last stretch of the game.
Captain Jack. He shouldn't be that hard, theoretically, since he only has three attacks. Except the two he uses with any real frequency are: 1) an incredibly powerful gun-type attack that randomly hits your party members (thus it has a chance that it'll hit your MC four times), and 2) a spell that heals him for over 1000 HP and removes all debuffs from him. He's not immune to getting charmed, but good luck making that stick to him. To make matters worse, his third attack deals "light" damage to the entire party, but it's Almighty element. This means you literally cannot resist it in any way, and just to add insult to injury it lowers your attack. This makes it even harder to heal with his gigantic Healing Factor. And if that wasn't enough, he starts the battle with two Pisaca demons who can inflict the Bomb status on your characters. It basically means that if you get hit, you die and take the rest of the party with you.
Maya. You know you're in for a hell of a time when using magic on her is answered with a 100% ACCURATE INSTANT KILL. This also extends to your guns, even though they technically aren't magic, as those too are grounds for getting one-shotted. However, that's only if you try to use its skills; regular gunshots are actually her weakness. Yes, she's weak to an attack that costs no MP and can be used whenever you want. Not that you'd be able to guess that, especially considering using Gun spells kills you. Not to mention she knows Illusory Ritual, which is basically this game's version of Red Capote (Read: maxes out accuracy and evasion) and all the -Dyne spells, which are boosted through using her different Gate spells.
Before even Ouroboros, there is Asura. This one can be especially unpleasant because all the parasites you fought previously were annoying but not especially difficult, lulling the player into a false sense of security. While he carries a weakness to Ice, he has a very annoying skill by the name of Asura Roga. Remember earlier in the sector where much of the Strike Team was affected by the Delphinus Parasite? Well now, it's your turn to experience it firsthand! Asura Roga can affect the entire party with the Rage ailment barely seen anywhere else in the game at all; Rage boosts afflicted party members Attack, but it also causes them to attack randomly either the boss or their allies. Very often the player will find that their own party wiped each other out, or came close enough so that all Asura had to do was essentially sneeze at them to win. Sure, you can spend your turns curing everyone of Rage (assuming the MC isn't affected and has the appropriate items, and/or a demon ally has a skill that cures it), but by the time everyone is healed up, Asura may use it again. While he also carries two more powerful attacks Ashura (powerful random target Physical attack that can hit multiple times) and Black Flame (basically Maragidyne except—again—hitting random targets), both of those tend to be much more bearable than Asura Roga.
The final boss of the Chaos path qualifies. While most of the fight isn't so bad, the boss occasionally breaks out an unblockable one-hit kill move, meaning all your work was pointless if it connects with you.
Digital Devil Saga
Camazotz from the first game, mainly because of extra-turn spells and ZOTZILAHA BANE, which can't be defended against and turns you into a bat, which has hideously low stats and a large Force weakness. Three guesses what all of Camazotz's damage-dealing attacks's element is. Void Force would be your only saving grace, but Zotzilaha Bane apparently overrides all resistances to Force with its weakness. Camazotz's downfall is that it has terrible HP for a boss, so if you aggressively assault him he'll fall like a pile of bricks before he can trash your party. Assuming, of course, he doesn't get overly lucky when he starts spamming Beast Eye. It seems appropriate for a boss which is named after a Mayan god of death.
For series veterans, Vasuki. Adjusting equipped skills to handle what the game throws at you in each dungeon and boss fight & taking advantage of the combo system makes the game grind-free until the bonus content and makes a Low Level Run to quickly advance the plot very doable until the player hits Vasuki. He uses ice and electricity, both elements that freeze or stun characters, allowing him to critical hit them to death. The player can only shield against one of them at a time (at that point), and Vasuki's AI is smart enough to attack with whichever isn't blocked, meaning he won't lose turn icons that way. To top that off, he's capable of using two unblockable megidolaons in the same turn. If the player is underleveled, they won't have the HP or magic stat to survive fighting him conventionally unless they go and grind or already made the effort to acquire Null Phys, which can sucker the AI but first leaves the player vulnerable to Vasuki's powerful ice attack.
Orochi, who has to go to reach an item required for the Metatron fight. He has absurd amounts of turns, one for each head. Much like Mot above, he likes spamming Makakaja, potent Almighty attacks against which you have no protection, likes to exploit weaknesses, is no stranger to strong physical attacks, and nulls or absorbs most attacks and has no weaknesses. The fatal flaw? Orochi has horrible MP for a boss, and will constantly deplete itself. When this happens, he will cast MP Drain to restock its own tanks and go back to pounding you, but Null Mute will negate the attack, leading to no extra MP for Orochi; if everyone has it, coupled with Null Poison, Orochi will lose most of its arsenal. Once this has happened for long enough, optionally using Dekaja and Dekunda once or twice or just plain being careful with buffs and debuffs, Orochi will be essentially die of MP starvation, spamming Mad Rush (which can be Debilitated into oblivion).
Kartikeya in the sequel, which pounds on you with an assortment of powerful party-wide attacks and raises a barrier that makes it nigh-impossible to hit the boss, pretty much whenever the boss feels like it. Repelling its own spells or using electric magic is guaranteed to hit it and break the barrier, but that's easier said than done.
Vritra is often cited as also That One Boss of DDS2. Especially if you go into battle expecting him to be weak against ice attacks. Many a gamer has burst a blood vessel to see the attack absorbed text appear on the screen and watch their whole battle plan fall apart at their feet as the very same magic from their precious strategy is flung back at them. Twice as hard. And then Vritra calls you an idiot for thinking it would have worked. He also has a pair of tentacles that protect him from damage and must be destroyed before you can actually do damage to him. (These naturally regenerate after a couple of turns.) To top it off, he has a skill that has an extremely high chance of freezing your characters. In DDS2's battle system a physical attack against a frozen target is an automatic critical, (Which not only causes extra damage but gives the attacker an extra turn) which Vritra is more than happy to exploit.
Abaddon. The thing changes weakness, swallows your party members leaving you with two characters for most of the fight. Good luck not getting Argilla swallowed when he's weak to earth, because if you can't exploit his weakness and gain extra turns you will be spending ALL of the turns you have healing/reviving, and if you don't damage him enough in 4-5 turns he'll use a ridiculously overpowered attack...Om mani padme hum.
While he IS a Final Boss, Great Father Nyarlathotep in Persona 2: Innocent Sin is VICIOUS. He gets five attacks on his turn, and can easily bring a prepared party to their knees. Unless you are at incredibly high levels, you are going to get destroyed. The only breather he gives is that sometimes he will switch over from attacking your HP to your SP. Use that time to deal as much damage as you can, because once he targets your HP again, every single effing turn will be spent healing.
Persona 2: Eternal Punishment has "The Metal Trio"—golden statues of Jun, Eikichi, and Lisa, who were born out of Tatsuya's guilt. Like the Sylph battle example from Tales Of Symphonia, this is a team battle, your party against them. While each character doesn't have a huge amount of HP, each enemy is immune to physical attacks, and possess unique high damage spells that target all party members, and to further twist the knife, Eikichi's 'Bloody Divorce' has a high percentage of causing instant death. "Jun"'s 'Terror Fortune' special can inflict almost every single freaking status ailment on everyone with next to no fail, often leaving you utterly helpless.
In Persona 3: Atlus apparently decided to go back to its roots; like in Nocturne, pretty much every boss is difficult to kill.
The Updated Rerelease, FES, has the final boss in the sixth level dungeon of The Answer: The Conceited Maya and the Jotuns of Blood. The Maya has a large number of hit points and will absorb damage from physical attacks, meaning your party is restricted to its Elemental Powers. However, every time it loses twenty-five percent of its health, it summons Jotuns of Blood, which are nearly as difficult to kill and are invulnerable to elemental attacks. Furthermore, they possess all of the high-level attacks (both single and multi-target) for the four main elements and will absolutely shred your party's weaknesses. It is possible to take a party with no weaknesses (the Maya and the Jotuns don't know Hama or Mudo skills), and to fuse a Persona without any - actually, this is required, because if Aegis has a weakness, no matter what the rest of the party has, they will focus on her. And remember, We Cannot Go On Without You.
The combo of Strength and Fortune, the October full moon bosses. Fortune can hit you hard with its attacks - which are pseudorandom - and you can't even touch it until Strength's dead. Most of the other full moon bosses aren't that bad, but this is definitely That One Full Moon Boss.
And before them, we have Lovers, who is a douchebag. As you might expect from a giant Shadow heart, it specialises in Charm attacks, and will annoy you with Holy Arrow and Marin Karin. God help you if the MC gets charmed, because for some reason, nobody ever seems to want to cure it. And then it brings out its signature move, Heartbreaker, which deals huge damage to the whole party. Love Hurts.
Sleeping Table, the infamous boss from the fourth block, floor 135 of Tartarus. It was deemed difficult enough for most players that it earned a spot as a semi-optional boss (it's fought in the optional True Ending path) of Persona 4. Its physical attacks are nothing special, but it comes armed with Maragidyne (highest-tier, party-wide fire attack), Hamaon (light-based instant kill) and Megidola (second-tier, unblockable, all-party Almighty attack,) has no weaknesses, and has such exceedingly high defenses that physical hits deal pitiful damage. In addition to that, it is immune to status changes. No fear, no panic and not even Dreamfest can charm it. In other words, it will rain destruction on you and you cannot prevent it. When getting hit with Maragidyne is considered a breather, you know you're in for a lot of pain.
The World Balance from floor 236. Some players have complained that they thought that it was actually adapting to their decisions. Interestingly, you can use this to your advantage: if you throw up buffs constantly, it'll waste time trying to dispel them instead of attacking, allowing your party to just beat him to death.
Natural Dancer will destroy you if you don't look up a strategy. It just loves to charm your party (with an unusually high success rate) and has powerful all-party Garu attacks, and the only kind of attack it doesn't resist is Bufu (well, it technically doesn't resist physical skills either, but it will quickly cast a spell which reflects those back at you). It also bears mentioning that your wind-resistant party member, as well as a couple of the better wind-resistant/immune personae, have powerful healing abilities. Healing abilities which they will happily spam on the boss when they (inevitably) get charmed, meaning that even if you have a good setup to avoid being massacred by its wind attacks, you'll still find it extremely hard to damage the boss faster than it gets healed. Hope you enjoy farming magic mirrors...
If you thought the Natural Dancer was bad, then the Royal Dancers are basically that times three. In terms of straight-up attacks, they're actually less aggressive (in fact, they only have one skill that deals immediate damage), but more than make up for it by having almost every ailment-causing move under the sun; Tentarafoo, Poison Breath and Sexy Dance are just a few of their moves. They can use Patra, Charmdi and Posumudi if you try to use ailments on them, and they can also heal themselves. Oh, and the one actual attack they have is freaking Primal Force, one of the strongest physical attacks in the game.
The Final Boss deserves mention for being a shining example of Fake Difficulty in a game which is otherwise tough but fair. He's a Sequential Boss with thirteen forms. Twelve are normal boss fights, even a little on the easy side, but put together they take almost an hour to get through, and no saving in between forms. Then the thirteenth form likes to spam its unblockable hit-all attack, has 6000 HP, takes half damage from everything except the Almighty element, and will randomly stop your progress cold by using an energy shield that reflects everything. It takes about a half-hour to whittle down his HP to the point where he's finally had enough and busts out his ultimate attack — which, in most cases, leaves you flailing for a few turns trying to recover, and then dead. Hard bosses are one thing, but bosses that make you go through an hour and a half of A.I. Roulette and tedium before clobbering you are a special kind of sadism.
When he enters his final stage of the fight (low hp in his thirteenth form) he can use status ailment attacks on your whole team. Fun fact 1: Charm is a status ailment. Fun fact 2: You probably have a teammate with full heal around just to keep yourself alive. Fun fact 3: Yes, full heal is FULL heal. If you are unfortunate enough to have a charmed teammate use their full heal on the boss, they get all 6000 of their hp back. While he does remain in his thirteenth form, that thirteenth form completely restarts, which includes the energy shield and the hour and a half of A.I. Roulette.
The Brilliant Cyclops, fought in the second dungeon of The Answer. It's just one Shadow, and the previous fight pitted you against four. Besides, it's the second boss of the game! This shouldn't be too hard, right? WRONG. The only element it's vulnerable to is fire (it reflects everything else), it has very powerful ice spells (Bufudyne on the second boss of the game? Seriously?) and can summon Soul Dancers, which could be bosses on their own, by virtue of having Agidyne and HEALING SPELLS potent enough to get the Cyclops back to full health in two turns. It will summon those Dancers after he falls below 50% HP, and each time one dies, it just replaces them the next turn it can. There can also be two of them on the field at once, so they can either heal the Cyclops to full health in one turn, or have one incinerate your party and the other heal.
Shadow Kanji. This boss has been known spawned some... rather colorfulrants against certain things like his hugely powerful physical area attack, large amount of health, and, of course, that one son of a bitch who constantly gives him buffers and health restorers. Part of the reason he is so hard is that he comes at a time when you don't have access to top notch Personae (unlike most of the harder late-game battles), but he still has abilities that are devastating in their own right: Unlike Shadow Yukiko, who's merely a harder than average Wake Up Call Boss, and fairly manageable for a seasoned player, Shadow Kanji is powerful enough to quite easily beat any team with a lucky critical, or at least make it an extremely close battle. Persona 4 The Golden Nerfed him by giving his two shadow helpers weaknesses to Fire for one and ice to the other, and instead of using high tier stat enhancers, they only use low tier ones, and try to protect themselves more then they try to protect Shadow Kanji.
Shadow Teddie can be difficult because you most likely set up a team to simply deal with Shadow Rise and are not expecting a second boss battle right afterwards. Yukiko is a great healer and have her around to handle that job...except she is horribly weak to ice attacks, which Shadow Teddie specializes in and by extension is immune to, AND he has Mind Charge (which can power up his Ice attacks even more) plus Ice Break (reduces Ice resistance) and Marakunda (lowers party defense, which is bad for Yukiko due to being a healer). So, you are faced with a dilemma. Do you have the protagonist be the designated healer and drop Yukiko, or do you risk the ice weakness and bring your best healer along? As if this wasn't bad enough, you have the Nihil Hand move to deal with, which does nasty damage and inflicts the Dizzy status on the whole party — and if one or more of your party are already Dizzy, it's an instakill for them. While it has an obvious set-up and easy countermeasure (simply defending), towards the end of the fight you have less time to prepare for the attack and in a panic, you could accidentally do something other than defend. To top it all off, Shadow Teddie likes to throw out both Foolish Whisper (a Silence spell, aka prevents use of your Persona) and Nullity Guidance, a move that will ALWAYS crit and give Shadow Teddie a Once More (leaving you with even less time to prepare for Nihil Hand) and causes a Dizzy state, so hopefully you stocked up on Mouthwash before entering the dungeon and are prepared to spend an ally's turn to remove a status ailment.
Shadow Mitsuo will make you cry. He takes way too long and constantly gives himself a shield of 1400 additional hit points every few turns. He has a ton of attacks: he'll attempt to put the Fear condition on the whole party and then use a whole-party attack which kills fearful foes. Sometimes, he will precede Fear with Stagnant Air, which raises the susceptibility of status ailments. Worse, it will consistently attack with a randomly-chosen, multi-target elemental spell while its barrier is down; if at least one character is weak to the element and is knocked down, it will immediately follow up with the party-wide Megidola that will almost certainly kill at least the weakened character, if not everyone else. And in barrier mode, aside from a powerful normal attack (that deals Almighty damage), it can also use the party-wide Gigadyne and a "Bomb" attack that delivers medium damage AND inflicts Exhaustion status (SP drops with every action, like Poison does for HP) with 100% success rate if the attack hits. It's almost a relief when he uses the barrier form's ordinary attack, which hits between 170-240 HP when you're likely in the mid-300s.
Kunino-sagiri is a pain in the ass. He has a ridiculous amount of HP and can control your party members so they try to kill you if you're unlucky. The hard part is when he uses Quad Convergence, which powers up the strength of one element and makes the other ones do close to nothing if you attack him with it. He also ALWAYS uses Ma-Dyne spells, which hit the entire group. If you're willing to use up four Magic Mirrors and you get lucky, this can actually be turned in your favor and shorten the fight considerably. That supercharged Ma-dyne spell will bounce off your team and hit him four times, depleting roughly a third of his life bar in one turn. He won't always do this, but it's so sweet when he does.
Read up on all the Persona 3 and 4 entries? Welcome to the bottom, where we tell you that you can also play them on Hard, which gives every enemy in the game a guaranteed 150-200% damage boost at all times. When the Mooks nearly kill any party member in one strike, well, let's just say every boss becomes That One Boss. Oh, and for the Persona 3 ones not in The Answer that you breezed through on Hard? Get Persona 3 Portable. Welcome to Maniac Mode, which is Harder Than Hard, literally. Oh, and Maniac goes as far as to nullify all New Game Plus bonuses, so you can't go in with a Level 99 MC, which gives you 999 HP and SP. You start at Level 1, no matter what. Very Hard mode in Persona 4 Golden, known as Risky mode in Japan, does the same.
To add insult to injury, the compendium is outrageously expensive in Mania Mode, meaning your level 20 persona is suddenly 70,000 yen to pull out. This is particularly annoying when doing Elizabeth's/Theodore's requests, as they want you to make certain person with certain conditions. You pretty much have to fuse in order to obtain a fair deal of them, and it's expensive to replace your useful persona. This is also an Issue in Persona 4 Golden, though the Discount bonuses Margaret gives out lessens the damage a little.
Raidou Kuzunoha vs. The Soulless Army: Mishaguji. Resistant to physical, immune to bullets. Powerful, with at least two moves capable of knockdown. Knows Cursed Emission— an unblockable attack that leaves you (or your demon) paralyzed for much longer than normal paralysis, and Cursed Bolt— a wide-area attack that takes up a good chunk of the battlefield, and charms whatever it hits. If it charms you BOTH (Raidou is paralyzed by charm, but his demon actively turns against him for the duration), you better pray your demon doesn't kill you, or worse, HEAL MISHAGUJI.
Sukuna-Hikona, whose attacks aren't that bad... on the surface. But then it starts sending out attacks that paralyze whatever they hits, following up with a large beam that deals significant damage. As if that wasn't enough, if this beam hits your demon, and doesn't kill it by damage, it will seal the demon in its tube and you cannot use it for the rest of the battle.
King Abaddon continues the tradition with Amatsu-Mikaboshi, the Star of Death. He's basically Sukuna-hikona version 2.0, with even more annoyances. The major one being that 95% of the time he constantly teleports around the combat field, pretty much making him invincible. He also can use screen-covering attacks that do high damage even when blocked (or are just unblockable). And like Sukuna-hikona, Mikaboshi too can fire "Mute Ray" which is the beam that seals your demons with no way to cure it except ending the fight. Sure he's weak to Ice and Force, but he's only truly vulnerable when he's firing the beam, and it doesn't help that most of the time you can barely hit him.
In Devil Survivor, if a boss has 'Bel' in its name, you might as well just start screaming in rage and frustration now. Because once the fight starts, you'll be too busy crying to do so effectively.
And his flunkies not only respawn indefinitely and include such utter nuisances as Vidofnir (Drain, anyone?) and Basilisk (Evil Wave and petrification abilities) but are also fond of the Petra Eyes/Mazan combo, which can kill an entire party in one attack. Consider that in this particular mission it's Game Over if the Hero falls...
Belzaboul. His attack range is huge, and when you combine that with the small arena the fight takes place in, that means he can attack anyone in the field. And it gets better: He's surrounded by lesser demons, which might as well count as a small army of Demonic Spiders, due to how annoying they are. So, you'd want to kill them first, right? Well, do that, and Belzaboul replaces them with his flies. They go down easily, but have an attack called Spawn that inflicts anyone it hits with the Fly status. Anyone with this status will die one turn later and spawn more flies. And Belzaboul's normal attack inflicts Fly, too.
Right after Belzeboul, a hard battle on his own, comes Belberith, who is able to attack anyone on the field and regularly heals himself roughly 450 HP after each turn. On his own, he would be only somewhat obnoxious, but to even get close enough to attack him you have to activate two switches to lower a pair of platforms that reach the stage he is sitting on. All the while demons are being summoned from COMPs that were left on the ground, and the demons are capable of using Phantasma to warp around the field, blocking your way when you need to press the switches and cross the platforms to reach the boss. If you run out of MP and are unable to heal, the battle becomes unwinnable and you have no choice but to reset the game. However, if you manage to get a character across to Belberith's side without hitting both switches, the enemy will do it for you so they can chase you down. And Belberith is weak against Force attacks.
The battle against Belial is an unholy combination of Escort Mission and That One Boss. The stage is one that makes it difficult to reach him quickly if you don't happen to have any Genmas or Avians on your teams. Like every other Bel boss, he also has minions scattered all over the place. He can attack 3x in battle. And he periodically unleashes a powerful fire attack that hits every player character and Haru. Keep in mind that you also automatically lose the mission if Haru dies— and she can only take a couple hits from Belial's special attack before dying. The only saving grace in this mission is Belial's vulnerability to ice magic.
And the fact that he still only has an attack range of 1, unlike further bosses. With this in mind it you can simply make 2 teams that have a tyrant and a vile/dragon to shut him down almost absolutely, weakness to ice or not.
And if you manage to brave Belial and go on to Amane or Gin's route, the next day opens up with you taking on Jezebel, with your only solace being a free battle spot to grind on before battling her. Unlike Beldr, who only attacks once per turn (barring Extra Turns) and has some pretty weak attacks, or the vulnerable-to-ice Belial, Jezebel has no weaknesses—in fact, ice, which you most likely used against Belial, is one of the elements she's resistant to. On top of that, the battlefield in front of her is covered in lava that inflicts fire damage to a character's team upon the end of a turn. And like Belial, Jezebel gets three attacks, and one of her spells is Judgment, which takes away 50% of all targets' HP, often cast on her first turn to make her follow-up attacks worse. Hooray for ragequitting two bosses in a row!
On Naoya's route the day opens with the same fight - only since you made a rather large group of enemies, you have to fight through no less than EIGHT human foes (ALL of which have Evil Wave or Chaos Wave) to even get to Jezebel. Then the aforementioned Belzaboul and Belberith. We're not even gonna start on the sheer pain that is the final boss - which would not be bad enough to qualify for this trope under normal circumstances unless you're on the first playthrough with very little grinding. If that's the case, then it sucks to be you.
And the Final boss is even worse in Gin's route, because you have just commanded Babel to unsummon all the demons. Guess what, it did, and thus you have to fight it with your characters alone. Woe betide anyone who picks that route for their first playthrough. Thankfully, since Babel gets moderately depowered after your team loses all its demons, it's entirely possible for a character with high Magic (Yuzu and Amane are ideal) to beat it with a couple of overpowered Elec Dances. It's even worse if you take this route on a subsequent playthrough though, because you are likely to have relied on your endgame demons from your last playthrough to blaze through the whole game, leaving your human characters underleveled and unable to survive on their own.
In the Devil Survivor 2 Neutral route, the Law bosses aren't all that bad, but the Chaos Boss.....may YHVH help you, because this bastard is tough. In fact, not only does blatantly cheat by buffing his turn ratio out the ceiling, but the battlefield is set up so he can be surrounded by mooks while his possession of a Vile Arioch allows him to beat on you like a redheaded stepchild, his Divine Remiel allows him to replenish his MP pool (which he abuses to spam Megido at least twice), and he himself can revive his minions with an auto ability. There is also at least one demon on the battlefield always nearby that can throw on more healing, and most of the others have Evil Wave and Chaos Wave, so they can beat the hell out your deployed demon summoners from a distance, and about the only way to even the odds is to provide everyone with a demon that knows Chaos Wave, and even then all the enemy mooks can hit like a truck.
Actually, you can blitz through his minions fairly easily if you know what you're doing. The problem is that this only makes Yamato faster, leading into a situation where he can get turns non-stop and achieve a Total Party Kill. Did you think you could use Phys Amp+Pierce+Multistrike to take him down? Haha, no. You see, Yamato has Repel Phys, which means that you will be killed by your own attack. Seriously, this is a Luck-Based Mission of the worst kind.
And that battle is made EVEN HARDER in the Anguished One's route. Imagine, instead of him getting his turn absurdly quickly, he instead summons a magic field that damages your HP and MP. If you kill any of the demons, the Norn just revives them with full health. As for Yamato himself... He has Prayer (Full HP and status restoration, so no Curse to prevent it), MEGIDOLAON (strongest hit-all attack in the game), and Drain (HP and MP steal). He halves all damage excluding Almighty, and has the Ghost Purple Mirror and Kishin Zouchouten. They can use Possession (Inflicts Curse, which prevents you from healing), Judgement (Halves HP), and allows him to attack twice. Yamato also has Magic Yin, which increases magic by 50%, but doubles cost. However, Drain offsets the cost while still doing massive damage. End result? Good luck trying to go for the Unkillable title.
The battle against the Osaka faction in Ronaldo's route can be an absolute sheer wall thanks in large part to Keita. The kid's got a downright vicious combination of Rage Soul and Attack-All, allowing him to level entire parties with a single attack. And if for some reason you survived? He can initate battle twice thanks to Zouchouten! What's more, the battle's on a time limit. May as well pray to the stars for salvation, because Atlus sure isn't showing any!
On the 3rd day we have Ronaldo. At this point you've fought two of the Septentriones, so you figure, "How hard could some human boss be?" Very hard, as it turns out. A particularly nasty Wake Up Call Boss, Ronaldo possesses a Baphomet with no weaknesses, a Suparna with only one, and he himself is a tough customer. His Baphomet gives him long range attacks and his Suparna allows him to teleport and make up for the loss of movement. He and his Baphomet both possess Drain, a devastating skill at this point, since it heals them, removes your precious MP, and is an almighty skill. The only good thing is at first he won't do anything, but your demons will drop like flies once he does. You also have to prevent his lackeys from escaping, which means you aren't at liberty to move around as much. Another problem is that at this point, you don't have any kind of way to revive fallen comrades. You fight Phecda, the third Septentrione, afterwards, but Ronaldo joins up with you at this point, and can easily beat the crap out of the Eldritch Abomination.
The Anguished One's route starts with only you and The Anguished One against all three factions, leaving you with two teams to start with (The Anguished One is, fortunately, extremely hard to kill, but weak offensively). First up: A match against Hinako, Jungo, six-seven backup squads and a level 76 Shiva, which is utter murder on a first playthrough (fortunately, Shiva goes away if you beat Hinako, making fighting him optional). And if you didn't rank Hinako and Jungo up to level 4 fate (or, Polaris forbid, managed to get Jungo killed, which is fairly easy if you don't know exactly how to save him), they don't join up. That makes your next stop your two teams against Daichi, Io and about eight other teams with an assortment of high-level demons, and Io has the stats of a boss on her own *and* boosts all her allies with extra attack power and turn speed. Good luck with that.
On Day 7, we have the Septentrione Benetnasch. First off, you can't summon any demons mid-fight because Trumpeter is using his jamming song to keep Benetnasch from dispelling the demons you already have. Second, Benetnasch is completely immune to all human attacks, so you'll have to rely on demons to do any damage. It reflects Physicals, so the Game-Breaking strat of Tailwind+Multistrike doesn't work. It has two forms, the second of which gets high level physical/force attacks and is the first boss to use Dragon Eye (giving it three attacks every turn). There are Megrez buds sitting around doing their usual full-map earthquake damage, and after you get so close Benetnasch fires four of them straight into the vicinity of Trumpeter (you get a Game Over if they kill him, by the way). And even if you do beat Benetnasch, all it does is break into four segments, each with their own high-level magic and special abilities that correlate to the seven Septentriones. You need a well-balanced party to stand a chance, and if the wrong character dies you might find yourself unable to finish off the final fragment, in which case it's back to square one!
Other Shin Megami Tensei
From Last Bible, we have Minotaur, who is effectively the third boss in the game, the Zodia/Mephist Boss Rush, and the fight with Vaerial before you get to Terra.
Not Shin Megami Tensei
While only an action game in the loosest definition of the word (I.E., a game focused mainly on action-y things rather than slow, measured things), the racing game Snowboard Kids 2 has only three bosses... and every single one of them is a That One Boss. It's not enough that you have to beat them to the ends of their respective race courses—hard enough, given that they're much faster than you could ever be. It's not enough that they constantly drop debris and other things to slow you down. It's that you also have to drop their HP to zero, with an array of non-homing, hard-to-come-by projectiles. And they're often so far ahead of you, getting a straight shot in is hard.
On top of that, the final boss will actually regenerate three extra HP after you manage to beat him down and become much faster. Since this usually happens near the end of the track, it's very likely that you'll deplete his "normal" HP bar only for him to sprint to the finish at the last minute.
Etrian Odyssey II made the first game look easy by taking out all of the cheap moves you'd use to actually survive well. Even the fact that some bosses cause mass confusion is nothing compared to the terror of Colossus. It was a hard enough fight as is due to massive damage output, resistance to every element, Massive Damage magic counterattacks, and the occasional defense debuff, but those poor people trying to use Buff-centric parties had no idea that having buffs active triggered Mad Rush, That One Attack that does about 40-80% of a max-level character's HP (depending on class) and simultaneously will multi-bind your party, likely preventing your healer from even being able to do anything...
Etrian Odyssey IV has some pretty hard bosses already, but ramps up the difficulty to unfair levels with the second boss, the Hollow Queen, an unholy fusion of Flunky Boss, Wake Up Call Boss, and the good old-fashioned Atlus experience we've all come to know and love. She constantly summons powered-up versions of herHollow minions, while hammering entire lines with her Darkness Wing and Dimensional Cut attacks, and swamping the entire party with mass confusion and the dreadful Icy Aria. And, both her and her minions are borderline impossible to hit without first binding their legs. And unlike the Berserker King, bindings do decay on her, and even binding her head won't stop the infernal Lover's Breath ability from removing every binding and ailment you can inflict on her in one fell swoop. Not even Wufan's involvement can abate the holy terror of this boss fight.
Dr. Zero was no pushover, either, with one of his robots knowing the ultra-powerful Alpha move.
Of all people, Bisco can give you a good thrashing with his Hexbot. It uses a super strong Evil-type attack, and at this point in the game there's not much that can resist it.
Kamat's army; since the minigames you're required to play at this point were not required earlier, there is a strong chance that you will be entirely unfamiliar with how they work.
Mr. Wild, the Legend5, has strong Robopon that can cause status effects as well as deal heavy damage. And he stole your Robopon, Dosbot, for the fight.
In the second game, Circe counts, with her Robopon being fast and powerful. And unlike in the previous game, when you die you don't continue. You get Game Over. Cue hours of level-grinding rage.
Insector can be particularly troublesome as well, due to the fact that he comes right after Circe and most players will not find the only healing Robopon within the labyrinthine Pond Garden. In fact, most bosses after Mr. Gait have a tendency to have obscenely strong Robopon that use Standard Status Effects and software to decimate the player's team in a rough, aggressive blitz, much like Circe.
Give Maskman enough uses of Shield, and all attacks on his Robopon do 0 damage.
Dr. Zero Senior, the final boss of the game, is harder than the Bonus Bosses.
The first game shows up a good example: Inferno Kirin who is exactly the same as before but with a VERY large HP that is sure to break one or two weapons your if you don't have Weapon Shield on. Also it deals extremely high damage with ANY attack even if you have high def values.
Bonus if you use the strongest weapons in-game which have the lowest DUR.
Actually, Inferno Kirin has very obvious (and unique) movements preceding all his attacks, which serve as hints as to which attack he'll use next, allowing you to dodge as necessary. Granted, you'll probably get killed repeatedly the first few times as you try to figure him out, but the massive EXP you get for killing him justifies learning his attack patterns; it's a given that you WILL level up more than once per battle, at least till you're nearing the maximum level.
In the third game V.E, Jade and Tier will just make you cry with their overpowered multi-hit attacks. ESPECIALLY V.E and her Axe's skill Aqua Burst that can sweep your HP to almost nothing if fully hits you.
Horrza, the Area 9 boss from XEXYZ. He is quite possibly the closest thing to a Bullet Hell boss that the NES can actually produce. He also has much more health than previous bosses would indicate he SHOULD have, and kills the player in 4 hits. Very few players have killed him without emulator tricks. Owning him on a console is practically a Bragging Rights Reward in its own right.
Dragon from 3D Dot Game Heroes. He does good damage and takes a ton of hits to kill, even with the most powerful sword available to the player, even IF it's fully upgraded. Also blocking his fireballs sometimes causes the player to take damage anyway. Later in the fight, it randomly starts flying and smashing down, creating a giant shockwave that's difficult to dodge.
Kraken's not too bad of a fight normally, but trying to book it in the Bestiary is an exercise in patience. It takes a whopping 70 hits with the Bestiary to book it, but this is relieved by the fact that its tentacles count for the total...Except they have terrible Hitbox Dissonance and randomly deal damage for no reason at all. And the head only pops up in a few spaces, and the arena is composed of islands with Wire Rod posts, making it an endurance match for booking.
The Thaumamachine in Radiant Historia fought in the Alternate Timeline's third chapter is one of the first bosses in the game to bring out the good old-fashioned pleasant Atlus experience. By itself, it has three attacks: a normal physical attack, Bull Claw, a multi-hitting physical attack that targets one character, and All Crash, a Wave Motion Gun that hits the whole party for roughly a third of their health bar. The real pain are the bombs that it constantly summons, which do nothing except blow themselves up, dealing severe damage to whoever's targetted. Trying to chip away at the boss's health while destroying the bombs before they blow up is quite a painful experience, because if you can't keep up with your healing for even a second, the pain will pile up alarmingly fast and it's time to say hello to the game over screen.
Rosch can plow through the bombs if you know how, but it's heavily likely he won't be leveled high enough to one-shot them if you've forgotten to train with him (and the enemies here aren't slouches either). If you do take them out, most of the time it'll use its next turn to summon more bombs. In addition, there's almost no way to easily take out all four of the first set without them self-destructing. Unless you get the gimmick (Electric Trap, Gull Swing, L/R Assault), you're in for hell.
Any time you see a Giant Spider, it is a sign that you're in for a ridiculous amount of pain. All of them have very high attack stats and an area-of-effect skill that inflicts status problems, and worse, they take up the entire grid, making Aht's extremely powerful traps completely useless. The worst of the bunch is the one you have to fight with Aht as your only party member.
There are a number of stupidly hard bosses in Catherine, but Doom's Bride arguably is the worst. First of all, you fight her on a Ice Level, where if you slip on ice off the edge, you die. Second of all, she is very fast at climbing compared to other bosses before her. Third, she has a move that causes an avalanche - if you are caught by this you are swept down to a lower level until it stops, which is potentially lethal. And lastly, she brings Fake Difficulty on with her cyclone attack. Removing random blocks from the level to hit you with and making it difficult to see what's going on.
Catherine herself is frustratingly difficult, seeing as you're forced to climb withKatherine, as well as Vincent. This new character is much slower than Vincent, can't cliff hang, can't use power ups, and is not able to be directly controlled. Instead, you have to scream at her to stay put or move to you while Catherine is chasing you up the stairs. You're forced to stand still several times over in the boss fight, and if Katherine dies it's game over. Often times you'll find yourself having to provide multiple climbing paths in the hopes that even ONE of them will be usable.
The Final Boss of Master Of The Monster Lair isn't particularly hard... providing that you spend nearly as much time you've already spent on the game to get to him farming for items to increase your strength. The Devil Lord has such ridiculously high defense compared to every other monster in the game, in fact multiple times more than any other boss before him, that without copious amounts of grinding you'll be hard pressed to deal more than one damage at a time outside of weapon specials... and he has an attack that he deploys when he's down to his last third or so of health that WILL heal more than you'll deal in a single turn (in fact, try upwards of five). Oh, and did we mention that he has over 1000 health? All told, he's a difficult boss and he can take around an hour to bring down.Thankfully, with all of the post-game equipment unlocked after beating him, fighting him when he shows up as one of the random bosses on the 20th floor is significantly easier.
Triti in the earlier Trauma Center games. Getting rid of it without using the Healing Touch or having extremely fast hands is like trying to punch out a brick wall. It's even worse in Under the Knife, since you need to cut it out before extracting it, andusing the Healing Touch absolutely destroys your rank.