The Age of Decadence is insane. You aren't playing the average videogame superhero, no. Its Turn-Based Combat is always lethal. It takes Save Scumming to clear some fights, others are simply unwinnable. Even with a well-built character, you will die. Even the loading screens tell you so. Oh, and designing a good character is up to Trial-and-Error Gameplay to figure out all the skillchecks you need to pass.
Digimon World 3 was released by 2003 but had several quirks one would expect to see in the first-era RPGs. The enemy set changes brutally from one area to another, and if an incautious player take the wrong turn he may end fighting enemies that can defeat your whole team without getting damaged. Status effects are outright broken and bosses tend to abuse them, while you only get to learn such skills near the endgame. Every now and then you're forced to fight against a Giant Space Flea from Nowhere who is very powerful (woe you if you show up without full health), and some sections of the game are just impractical to figure out without a guide, to say nothing about special digivolutions that require specific stat training and digivolution levels.
Rogue Galaxy is an absurdly difficult game, because enemies dish out damage like crazy and none of your party members can learn healing spells. You have to rely on items to heal and using items takes stamina, which is subtracted from the same bar you need to attack, use skills, and move about the battlefield. If your stamina gauges run out, you have to wait for it to fill up in real time while enemies thrash you. Some monsters require specific weapons to kill, too. Oh, and this is a Level-5 game, so expect lots of Mimics—and in this game, Mimics automatically start you out with an empty stamina gauge and can spam a wide area of effect attack, wrecking your party before any of you can even move.
The World Ends with You, while manageable for most of the story, gets unusually difficult at the end. You fight several bosses in succession after you're last able to save, the last one possessing absurd HP totals, and one death sends you back to the checkpoint.
Final Fantasy II will chew you up and kick your ass simultaneously if you aren't levelling up your characters' abilities intelligently (and the original version didn't really tell you how to do so).
To make it really suck, in order to level your weapon skills and spells, you need to fight enemies of a rank that's higher or at least, not too far below your current weapon skill. How do you know their rank? In the Origins remake and further, you can use the bestiary in the collections menu under Config. In the original NES release, good luck. If you don't know the Rank mechanic, you can spend hours grinding on enemies and wonder why your spells and weapon skills aren't going up at all!
Final Fantasy III was already difficult on the Famicom, thanks partially to a lack of save points, justified by hardware limits. Then it was re-released on the DS, and rather than add save points, the best jobs were nerfed, and the bosses were granted double turns and much greater HP. You'll have to Grind, Grind, Grind if you ever hope to finish it. You are forced to beat the final dungeon and its five bosses in one go, with death meaning having to do it all over again from beginning, and even before that, there is Garuda.
The DS remake of Final Fantasy IV fits this to a T. While the original in the U.S. was somewhere between the Japanese release and the later Easy Type version, this is in a league of its own. To count the ways...
Enemies will murder your party outright when you encounter a new set. Either in sheer numbers (good luck with 6 death zombies) or because they have some powerful AOE spell that they can cast over and over, for free.
Encounters tend to happen every two steps, tops.
No amount of Level Grinding can save you... mostly because enemies give abysmally low amounts of experience points.
Items you need also tend to be scarce, and they're ridiculously expensive.
If you try to take advantage of known weaknesses (such as hitting Scarmiglione with Fire, which he is still weak to), the bosses will all counter with an extremely powerful attack that can outright kill most of your party.
Thanks to New Game+, though, the game is only somewhat difficult the first time. It becomes laughably easy the second and third playthrough.
Final Fantasy V can either avert this or play it straight depending on how the player wears his/her thinking cap. If you're not taking advantage of the many game breaking combinations available to you; FFV can be a difficult game. If you're thinking or understand the use of the job system, it's one of the easier games.
The first few Dragon Quest games certainly qualify although all the games in that series are harder than average. Unless you're using an Emulator, you are going to get destroyed. It doesn't matter how good you are at the game, enemies curb-stomp you. Oh, and II? Hey, let's make a dungeon that's impossible to get through unless you use trial and error gameplay, or a guide! Did I mention that your spellcasters can't survive being glanced at by anything, and you're rarely told anything? Puzzles are of the Simon's Quest type, like "use X item at Y tile on the world map to reveal a cave" or "search a random tile for a vital item".
Ultima VIII: Pagan was infamous for its insanely frustrating jumping puzzles, which were likened to Super Mario from hell. Despite being an RPG, the developers decided to add "arcade" elements like running and jumping puzzles. The shoddy interface, poor physics, and the ridiculous save/load times didn't help one bit. The patched version fixed this by allowing targeted jumping and making the platforms stationary.
Odin Sphere. The game pretty much flat-out gives you infinite lives straight off the bat, and take our word when we say you'll need them. Almost every boss — and a fair few sub bosses — are That One Boss, and most four- and five-star levels are full of swarms of Goddamned Bats. It is made exponentially more difficult by the sheer loving detail put into the animation - which means you'll spend a good three seconds doing anything, from simple attacks to eating health items. Meanwhile you will be swarmed by enemies. Your character is knocked back by enemy attacks. Enemy characters are not, and will continue to attack through your attacks. Several levels also require a potion to prevent an automatic ongoing status ailment. The often stuttery frame rate will also prevent your actions from registering on a regular basis. Hello, Fake Difficulty.
Legend of Legaia. The "fighting game" battle system, while neat at first, quickly became extremely tedious and past the first couple dungeons, it made most NORMAL battles last close to five minutes. Worse, from the middle of the game onward if you did not spend obscene amounts of time grinding then you didn't stand much of a chance against the bosses.
Although over the last few years the difficulty of EverQuest has been drastically reduced through various measures, the game was originally deliberately designed to be as brutally difficult as possible. It allowed you to play by yourself until level 5 to 10 or so; after that, the game became rapidly harder to play alone until it became outright impossible for all but some specific character classes that can avoid direct combat. Some choice Nintendo Hard decisions:
Not giving you any in game map nor even a compass, combined with...
... Making towns extremely large and maze like (the wood elf town and dark elf town are somewhat legendary for this), to say nothing about dungeons.
... Starting night blind races in incredibly dark zones (Toxxulia Forest).
Making it so that if you discover you need to flee a battle, you cannot (due to the game slowing you down when you run low on health, and increasing the chance of you being stunned when attacked from behind)
Oh yes, and mobs never, ever stop chasing you (unlike, say, Wo W). The only way to escape is if you load into another zone, or the mob dies, or you die... or you aggrodump the pack onto some other poor, unsuspecting player. The last option is a bannable offense, by the way. A panicked cry of "Train!" means something in this game.
Requiring players who ARE grouped together to spend literally weeks just getting keyed for certain dungeons (finding random items that allow you to finish a quest for a key, often with drop rates of less than 0.1%)
Making your character lose all their equipment upon death, requiring they find their way back to their corpse, without any equipment.
Making characters lose 10% of a level upon death, undoing literally days of work for one mistake.
Having powerful aggressive enemies in low-level zones, such as Level 30 griffins in East Commonlands, a zone where Level 12 players ventured.
Some levels (the infamous "hell levels") require 4 times the amount of XP to progress through, meaning the 10% of a level upon death becomes, essentially, 40%
The later expansions were increasingly geared towards the 1% of the player base which had finished the previous expansion (the so called "über guilds"), meaning that there are rapid plateaus of difficulty — the idea being that you are expected to spend months "farming" bosses by killing them over and over in groups of literally dozens of players to get the equipment required to take down the next plateau's bosses. Due to the game originally being envisioned as a Pay Per Hour system, as most online games were when the game began development, some of these decisions were extremely suspect.
And if that isn't insane enough, nearly every other MMO afterwards seemed to think that all of the timesinks, frustration and the kind of game design that would be considered horrible in a single-player game was a good thing.
All that being said, EQ has been majorly nerfed over the years. The game has a compass and a rudimentary but functional map system, corpse runs have been done away with completely, exp loss on death is minimal, hell levels no longer exist and leveling in general is far easier, and mercenaries (computer controlled heroes you can hire) were added to make soloing possible.
Vagrant Story has a system called Risk points. The higher the Risk, the more damage you take (and dish out) and the worse your accuracy. At 100+ Risk you'll be missing four out of five times. And the way it raises is with successful combo attacks. This makes Vagrant Story probably the only video game in history that actually punishes you for playing the game well. Most of the random enemies encountered are even harder than bosses, because some weapons don't work on them at all due to elemental and weapon attributes. You also have invisible traps AND out-of-the-blue enemies in inescapable dungeons. Not to mention the final boss has a special attack that can kill you even if you have only 3-5 points of Risk Points and it cannot be blocked with magic buffs. And the enemies that can use an instant death spell on you... and you're only controlling one person for the whole game.
The supposed "first level" missions in Icewind Dale for the PC were so difficult and so prone to cause the death of the PCs that most new players to the game were told "right after you begin the game, use the cheat code to boost yourself to third level.''
Worse are the later Single-Character missions, especially (of course) at Hard difficulty. Just when your party is balanced enough at rock-paper-sicssors tactics to make it through the main game, you have to pick a single character to survive a long sequence of varied types of enemy.
The Mysterious Dungeon series in all its iterations—Shiren the Wanderer, Torneko: The Last Hope, Chocobo's Dungeon, and quite a few others—exemplify this entire trope to the max. The entire game is based on the premise of Roguelike dungeon exploration, with many of the same specifications, in particular that the hero has but one life. The catch: you also can't save levels, gear, items, power-ups, nothing. If you should happen to die (and you will), you are forced to restart at a checkpoint with nothing but your fists and a moderately powerful healing item and Level 1 experience, usually with a dozen hit points. A single mistake can lead to rapid death, the dungeons are randomized and often "themed" (e.g. nothing but Scrolls, traps everywhere, constant damage due to heat), you must stay fed or the hero will die and quickly, monsters spawn infinitely, traps are hidden in the worst places, and the worst of it? When you finish a dungeon, you revert to Level 1 again, and in some installments give up all your equipment, essentially starting from scratch. Some give you a leg up, like allowing you to take a few items in or store things so they don't get lost when you die, but not much else.
The worst of the lot is the original Shiren The Wanderer on the Super Famicom. It had one checkpoint: a hut at the very beginning of the game. If you died at any point, you went all the way back there, and needed to slog through all the dungeons again to get back where you were, minus any XP or items. It's brain-breakingly difficult and often quite unfair.
If you poke around Ustream you can often find Japanese players playing Jokenji Asuka Kenzan, a sequel to Shiren, only much more difficult. It's not uncommon to see it modified to insane levels, like "no weapons" or "1 HP per level".
In Resonance of Fate, battles can be absolutely brutal because leveling up actually increases the amount of Hero Gauge points lost when taking Scratch Damage (it goes up every 1000 HP). The Hero Gauge is basically what keeps your party alive: you can use it for super attacks or refilling HP, but if it empties, your party becomes basically useless. Considering that the Hero Gauge increases are limited by the story, and people usually think that leveling up HP in RPGs is a good thing, the pacing is a recipe for disaster. Not to mention that the customization for weapons (the real way to get stronger) is also limited by the story. Oh, and the whole party goes down if one character dies. Oh, and retrying after a Game Over costs an increasing amount of in-game currency. And this is just Normal Mode—the game has seven harder difficulties to tackle afterwards!
Many old first-person RPG dungeon crawlers are ridiculously difficult by today's standards, what with having to make your own maps, teleporters that drop you into identical-looking areas, pitch-black segments of the dungeon, really strong monsters, secret doors indistinguishable from walls, and just about every other cheap trick in the book.
Etrian Odyssey tries its hardest to recapture this, with huge dungeons you have to map yourself, enemy encounters that are either extremely strong or love status effects, expensive equipment and items, and of course the infamous F.O.E.s. The Skill Scores and Perks system means you can freely customize your characters' skill builds, but it's all too easy to end up with poorly-built-up characters that make fighting more dangerous threats a nightmare, forcing the player to have their characters Rest, and Resting comes with a level penalty (-10 in the first game, -5 levels in the 2nd and 3rd games, -2 levels in the 3DS games). And you only get 1 Skill Point per level, meaning that every allocation decision counts.
Atelier Lilie: The Alchemist of Salburg 3, the third game of the Atelier series, has a reputation for being hellishly difficult compared to its contemporaries. It perhaps is not "hard" in the traditional, Battletoads sense, but getting anything other than a very "generic" ending requires that you plan out your entire approach to the game before you even start playing; you must plan what you'll do ahead of time in terms of whole game-years. And a lot of the endings require that you do a lot. The amount of planning required makes this one Nintendo Hard for a lot of folks and hurt the sales of the game.
MOTHER is often considered the most difficult of the series. A very high encounter rate that plagues you through out the game even if you're not trying to level grind, but you will have to a lot thanks to the Difficulty Spike found in later areas in which almost everything is a Demonic Spider. Word of God confirms that the final area is highly unbalanced due to wanting the game finished soon.
The 7th Saga is definitely up there. Monsters do grotesque amounts of damage to your paltry HP and give little experience or gold (and have unlimited MP of course), both spells and attacks fail very often. Oh, and there's a group of other adventurers roaming around trying to complete the same quest as you are, and are always a couple levels higher than you are. If you run into the wrong one at one of the forced fights with one of these guys, the game can be very nearly unwinnable.
MS Saga: A New Dawn's difficulty is okay until you lose the White Mage, Aeon, leaving you with only one effective healer with enough TP to handle the massive healing jobs. Tristan has Full Heal, sure, but he'll be busy spamming Fin Funnel before he has a chance to use his very low TP to heal the others. Upgrades are extremely expensive, and you'll be stuck with very underpowered suits by the endgame unless you do serious Level Grinding to take on numerous cloned boss machines and Burning Gundam in order to get stronger units. Bosses and crystal marked enemies hit very hard and merciless due to the fact that you must be able to handle their fixed action patterns by that time.
Many of the early Wizardry games are known for their ruthless difficulty. Many of the puzzles are nearly intractable without a guide, in battles you are often hugely outnumbered and can be (very) easily incapacitated in a single turn. The worst offender is probably Wizardry IV, in which levelling was literally impossible (you had to complete the dungeon level to increase your abilities), and featured many puzzles of rather maddening difficulty. Even getting out of the first room of the first level requires a degree of off-the-wall intuition. Wizardry IV is often considered to be one of the most difficult CRPGs ever made.
This game was difficult by design. Wizardry IV (in which you play the original Wizardry's Big Bad) was unashamedly touted right on the box as "For Expert Players Only". Not only was it Nintendo Hard, but it also featured elements of Trial-and-Error Gameplay.
Both a Touhou fangame and tribute to Wizardry-style CRPGs, Touhou Labyrinth may not have permadeath, but it does feature absolutely unforgiving enemies. It's common for bosses to tear you apart the first few times you attempt to fight them, and on later levels of the labyrinth, even normal enemies will be absolutely hellish to fight. As if that's not bad enough, the game's superbosses will rip you to shreds unless you're prepared to level grind like crazy.
Demon's Souls. Yes, it is insanely, frustratingly, tear-inducingly hard, but it's because it's a game that DEMANDS mastery. A dedicated (and PATIENT) player will slowly inch his/her way through the game, slowly learning stages inside out and building his/her character up. With persistence, the player might even thrive. But after beating the game, it's new game plus time, which is even HARDER!
And after beating that, it's on to New Game++. And then New Game+++. There is no known limit. While the jump in difficulty between everything but the first plus is lower, there is no limit to the amount of pluses, and it gets harder each time.
The tagline for Dark Souls is "Prepare to Die". It's not kidding. Even the weakest mooks can kill you in seconds if you're careless. And many of the bosses could be considered examples of That One Boss. The environment is also trying its best to kill you, with traps and bottomless pits aplenty. Level grinding only gets you so far, the game will punish you if you don't learn from your mistakes. And just when you think you've got the hang of things, New Game+ ramps up the difficulty.
Dark Souls II is somewhat easier than the original on a first playthrough. Then New Game+ outdoes the first game big time. In addition, the Lost Crowns Trilogy DLC puts the vanilla game and the first Dark Souls to shame. The Scholar of the First SinUpdated Re-release takes this trope Up to Eleven - for example, now there's a freaking Guardian Dragon (a late game boss fight/Degraded Boss) in one of the very first areas.
Lords of the Fallen takes many inspirations from Dark Souls, including the sheer nightmarish difficulty. On some occasions it can be even harder due to the much slower speed of the combat. Players have to learn the positions of enemies as they progress through the levels, or be cut down. Bosses have patterns, but it can take many deaths before they can be learned and exploited.
The story mode of Pokémon Colosseum is probably the most difficult in the "main" series. Because of the game's focus on "Shadow Pokemon" and snagging Pokemon from trainers, there is an abysmally low pool of Mons to choose from—less than fifty, in fact. The fact that you have to steal Pokemon from trainers means that while trying to catch Pokemon, the trainers will be assaulting you with their own. Bosses have Legendary Pokemon at their disposal, and unlike the main series utilize actual strategies beyond Poor, Predictable Rock. The sequel, XD, dialed back the difficulty significantly, although it still does have you catch seven high-level Pokemon, mostly Legendaries, in a row without saving.
Absurd difficulty can be found in the Pokémon Mystery Dungeon series, although these are mentioned under "Roguelikes."
Pokémon Stadium 1 and 2 is the crowning example for the Pokemon series, with round 2 in particular being infamously difficult. The stadium cups have some diabolical strategies, and Gym Leader Castle has eight gyms that specialize in their gym type, with some incredible team synergy, and underlings that generally use Pokemon that counteract's the gyms weakness. But its their AI that makes them truly Nintendo Hard, as they will switch when at a disadvantage, and often have good selections to whatever you choose. Because of this, they are often accused of cheating, sometimes with the critical hit rng, even though it is a different critical hit formula. No other Pokemon game (or even game mods of Pokemon) come anywhere near the difficulty set by the Stadium series, making this a standout example.
This deserves more elaboration. In the first game, enemies were using strategies or moves that abused the short sights of the Gen I version of the game. Wrap and Fire Spin can and will trap your monsters for the entirety of their LP bar. Toxic and Leech Seed sapped health away in large chunks while you mysteriously missed with Psychic. This is when you're not dealing with obnoxious cheating such as a trainer in the prime cup who decided to load up really fast pokemon with one-hit kill moves that hit really hard. Gen II was obnoxious for a different reason. The movesets on average were fair and balanced...until round 2 came along and you were wondering how did Raikou learn Thunderbolt (Crystal's move tutor, which Stadium 2's early purchasers didn't get to just then). Gen II alao had one of the worst (if not THE worst) TM pool in the game, and so required lots and lots of breeding for olympus monsters just to be able to stand a chance against the A.I.s perfect bred, perfect IV/EV stat distributed monster teams.
The web game Clash Of The Dragons has horrendous enemies, some that can easily kill you in one hit. To make matters worse, there are limited cards purchasable from the shop unless you bribe your way to victory, meaning that eventually you'll be walking up a creek without a paddle. And to add insult to injury, there's an Anti-poop-socking feature and tons of enemies, meaning that you can spend weeks trying to beat a single level or even a single quest.
Nintendo Hard is the default difficulty for any Shin Megami Tensei game. Rampant abuse of One-Hit Kill spells in games where you only need to lose your main character to game over, a spell naming system that practically requires the player to learn a second language to know what everything does (fortunately, the naming's fairly consistent, so once you learn the language in one game you won't have as much trouble in other games), and the frequent use of a "characters get extra turns for exploiting weakness" mechanic which can frequently lead to the player either mopping the floor with a tough encounter or the easiest encounter annihilating an entire party before they even get a chance to move. Later games tone down some of the Fake Difficulty elements and add some quality-of-life features, and even add easy difficulty levels, but on default and above expect to still get wrecked by That One Boss and Demonic Spiders if you don't plan well or have a good party composition.
The original Megami Tensei deserves special mention for having its only HP-restoring items, Jewels, unavailable at item shops and only found by defeating a specific type of enemy (although luckily Jewels restore all of a character's H Ps). Also there are demons who have a special attack that permanently reduces one of your protagonist's experience levels.
The Fallout: New Vegas add-on Dead Money. You're stripped of all items in your inventory when you begin the adventure, so you have to make do with what you can scrounge up. The entire location is filled with pockets of poisonous gas that erase big whacks of your health (even if you have the perk that makes you immune to regular poisons About the poison The Cloud, the clouds of poison gas that inhabit the casino grounds, was made by the Mad Scientist group in Big Mountain to kill the Chinese and used the casino as a testing ground for it and the suits the Ghost People are stuck in. It's no ordinary poison.) and liberally salted with mines, frag grenades, and bear traps. The Courier has an Explosive Leash locked around their neck, which will go off if they get too near any radios or intercoms (some of which you can't turn off or even destroy) or if any of the NPC companions are knocked out at any time. And the only enemies around are Demonic Spiders that don't take extra damage from head shots, wield weapons that have a high chance of crippling a limb with each hit, and have a tendency to get back up after you kill themUnless you chop them to bits or let Dog eat them.
Fallout 4 itself is fairly easy. Survival mode, however is not. You start with a limited base carry weight. Ammo has weight now. You are required to eat, sleep and drink regularly. Diseases are rampant, which either require materials & Chemist or a Doctor to cure. Damage is severely lowered for you and severely raised for enemies. Rad Away (and other drugs) make you weak and susceptible to disease. Finally, there's no fast travel.
And if that wasn't enough for you, the Final Mixes for Kingdom Hearts II and Kingdom Hearts: Birth by Sleep offered an ability at the game's start when playing Critical and to later installments/versions: EXP Zero. Aside from bonus stats earned from boss fights to make it plausible, the most hardcore of players are given the opportunity to Low-Level Run the games on their hardest difficulties at Level 1; by the end game, pretty much everything can kill you in one or two hits if you don't have certain abilities and the sheer skill to prevent it.
Guild Wars 2 manages this on some of its jumping puzzles. Most have only one correct path which can be difficult if not impossible to spot on your own. Many jumps are extremely exacting, allowing only a slim margin of error for positioning and timing. Enemies are also present and can interfere with knockbacks, slows, crippling, and all other manners of annoyance. If you die without a partner, your only choice is to start the entire puzzle over again, which may also be required if you miss even a single jump.
One particularly aggravating puzzle has a ceiling located at just the right height so if you don't jump at exactly the right moment, you'll be knocked to the ground and have to spend a minute running back to the jump.
Mesmers can avert this with their Portal spell. By placing a portal at your feet just before attempting a difficult jump, you'll be able to zip right back should you fall, simply by placing another portal connecting to the first one. This tactic serves as a safety net of sorts. Needless to say, Mesmers are highly sought-after partners for difficult jump puzzles.
Super Adventure Box, a retro-inspired Game Within a Game, is clearly designed to evoke memories of Nintendo's golden days. While the main paths through the levels are relatively simple in comparison to the jumping puzzles, getting 100% Completion requires grinding through some especially exacting jumping puzzles. And that's before you enter Tribulation mode.
The final boss fight in Baldur's Gate: Throne of Bhaal becomes this if you have the Ascension mod installed. Amellisan is already a Marathon Boss by herself, but with Ascension she turns the fight into a Boss Rush by summoning the Big Bad and his Dragon from the second game, then summoning the Five-Bad Band of this game. Oh, and she keeps summoning her Demonic Spiders while this is going on. And all this can be potentially followed up by her getting Sarevok to Face–Heel Turn if you don't redeem him, impress him enough with your evil-ness, or use a mod to romance him and turning Imoen into the Slayer, which deprives you of two party members, one of whom is generally regarded as the best in the game. Have fun.
Every Bhaalspawn fight in Ascension becomes so much harder, to the point that the very first one is nigh impossible if you didn't import your party from the previous game and thus have to fight her by yourself. Yaga-Shura, for example, has his Healing Factor lowers slowly over the course of the fight instead of all at once, he can hurl fireballs whenever he feels like it, is accompanied by a quartet of powerful lieutenants, and his army at least doubles in size, turning into The War Sequence.
Robopon is published by Atlus. Enemies can be surprisingly strong in dungeons and the bosses can be obscenely difficult if you don't come prepared.
The second half of Mario & Luigi: Dream Team fits this trope to a T. Early on, it's not much harder than a typical Mario & Luigi game is by that point, but once you get to the Ultibed quest, the game ramps it up into high gear. Especially the giant battles. The first two aren't horribly difficult, but starting with Earthwake, they WILL mop the floor with you if you don't have pixel-perfect timing. Plus some of the mini-games have a Scrappy Mechanic similar to Beaver Bother.
On the other hand, you can restart battles as often as you like and even have an easy mode option for everything but the giant battles. Then there is the hard mode... which also makes the giant battles even more unforgiving and losing a battle means gameover.
Seraphic Blue has almost every enemy be a Demonic Spider capable of outspeeding parties that aren't overspecialized in speed. And later bosses don't shy away from very cheap party wiping attacks, to the point where the the main character is given a party auto-life spell just to ensure the Final Boss is remotely fair.
Most of Undertale plays fair. Even the final boss of the Neutral route (Flowey, who has not only taken over the game itself, but has transformed himself into a huge animutation-style monster through the power of the human SOULs) isn't that tough once you have his attack patterns figured out. For Genocide route players, though, it's a different story. Most enemies, and even most bosses, die in one hit, but the two bosses exclusive to this path are incredibly unforgiving: Undyne the Undying will wipe the floor with you, and Sans's attacks come so quickly and are so unpredictable that even an experienced player is guaranteed to, as he puts it, have a bad time.
Nocturne: Rebirth has difficult bosses that can easily wipe out parties that lack proper resistance to their elemental and status attacks. Normally, this wouldn't be a problem by most RPG standards, except that the equipment needed to resist these attacks are usually Rare Random Drops. While the main characters can grind for passive abilities to make up for a lack of gear, the familiars absolutely need gear to deal with anything they don't innately resist. Worse yet, familiars can't be revived in battle, meaning the main characters could be forced to fend for themselves against the bosses in the worst case scenario. And if the player wants to get the Brave Clear rewards, they'll have to beat the bosses at a low level, requiring them to be very selective when allocating skills, which can be difficult on a blind playthrough.
The Elder Scrolls III: Morrowind apparently frustrated a lot of people when it first came out, because they kept dying over and over fighting the first puny animals they met around the starting village. This was due to a combination of the complete freedom the game gave the players when choosing skills during character creation (leading many players to build characters with no combat skills already set to a useful level at the start), a badly designed combat system (a low-level player character misses often even when you clearly hit the enemy polygon), offensive magic being very weak at early levels (compared to physical fighting skills), and extremely aggressive auto-attacking wildlife. Also, it was notoriously difficult to find some quest targets in that Wide Open Sandbox game just based on the information given by the Quest Giver, which annoyed some players to the point of giving up early. Though others enjoyed the challenge and were in turn annoyed when the creators switched from in-game way descriptions to a simple target-seeking GUI compass in the following game in the series.
Star Stealing Prince has bosses that can easily defeat players that neglect buffs, debuffs, and resistances from equipment. Worse yet, most of them will know to change their tactics if they're suffering from certain status effects, as shown by how they use fewer physical attacks when blinded.