These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: Although technically a boss, Tyrantula otherwise fits this trope nicely, capable of entangling your characters and striking them all at once with its toxic venom.
Boa Bishops. Good Almighty, Boa Bishops. These things get two goes per turn, have a hit-everything attack that can destroy mages in one or two turns, an automatic sleep attack, very much avert Squishy WizardandFragile Speedster. And they show up in twos and threes, often accompanied by cyber spiders (Demonic Spiders themselves, what with their blinding and slowing moves, high attack, and needing magic to be killed) or freaky tikis (which lower resistance to Standard Status Effects and also have a blinding move). Oh, and if that wasn't enough, they also chase you instead of going in a straight line, and their snake tentacles/feet give them extra width so you can't even dodge or go around. Even level 99 parties can be quickly killed by these things.
There is one high level type of Sanguini, the "Genie Sanguini", who did not turn into a demon. "By some miracle", according to the bestiary. It Randomly Drops Saint's Ashes, an item which inverts cursed and dark equipment into their holy counterparts. Implied: The Genie Sanguini didn't become a demon because it ate a saint.
One of the Celestrians, just before Fyggbloom, mentions how the the Observatory floats directly above a wasteland that had once been a prosperous kingdom. This matches the description of Brigadoom, but also the Gittish Empire... and if it's the latter, the irony becomes horrible.
Game Breaker: Two things: Tension makes a comeback, but is optional. A fully tensioned up character, with buff spells, using a powerful attack can do 70-140 TIMES the damage of a standard swing — 7000+ instead of 80. Endgame bosses have an attack that specifically prevents this tactic, but bosses before the end of the main story do not. In addition to that, you keep skill points between switching jobs, meaning that if you level to 15 then switch jobs a few times, you can take one of the class's 5th, passive skill trees to 100, which then affects all jobs that character uses. Taking Courage to 100, for example, will make the character strong and tough even if they are a Mage. Taking a weapon's skill to 100 will make them vastly stronger when using that weapon (+ 60 attack power when most weapons at the time are giving around 27) than they "should" be. Later, doing this up to level 38 (which is when jobs give the first 100th skill point) will allow you to do this with *multiple* skill trees.
And the legacy and grotto bossesrequire you to do most of this stuff to have a fighting chance. And most of them have an attack, Disruptive Wave, specifically designed to counteract the first one.
Forbearance, the ultimate Paladin skill, makes your Paladin take all incoming damage for the team. So in effect, what you can then do is outfit your paladin with the best gear, dedicate one character to healing, and have the paladin cast Forbearance every turn. While this means your paladin will take 4 hits every time the enemy casts a group-targeting spell, it also means that your healer only has to heal one target. In addition, it means that damage reflection skills (such as the Fan's Reverse Flourish or Shield's Magic Mirror) will reflect breath and magic four times.
Against metal monsters, Have A Ball is right alongside four Falcon Blades for efficiency, as it fires six or seven low damage attacks, randomly distributed among the enemies. Gets even better if you start the battle with someone's tension at fifty, in which case they're dealing four damage per hit against monsters that have less than twenty HP.
Goddamned Bats: The Metal slimes. In order to unlock the Armamentalist vocation, you have to kill two with a wizard ward barrier up. Easier said than done, given the fact that Metal Slimes have a tendency to run before you can even get their health down to the point where a mage can finish them off. (Granted, mages can inflict 1 damage, and you can give them Metal Slash, or exploit abilities).
Just about every enemy that insists on chasing after you, no matter how weak they are, beginning with the Teeny Sanguinis around Angel Falls. Especially annoying in the Bad Cave where every enemy is one of these, and in the Bowhole where you can expect the Sculpture Vultures to get in the way of Liquid Metal Slime hunting. They do eventually start running away from you once your level is high enough, but you're normally able to easily decimate them long before that arbitrary point.
This trope is very much at play in the grottoes. While searching for treasure, monsters pop up everywhere. There seems to be a particularly high number of large monsters in cramped hallways. You can use holy water or Vanish to stop the monsters from chasing you, but if you bump into one, you still get into a fight and the holy water wears off. This becomes particularly irritating when you reach very high levels, and the monsters on the upper floors of the grotto are weak. You get knocked into a fight with a monster that is just about worthless and not at all challenging. Not that bumping into the tough monsters lower in the grotto is any better.
Les Yay: Ivor is bitterly envious of the MC getting attention from Erinn (as he clearly Cannot Spit It Out), even if the MC is female.
Moral Event Horizon: King Godwyn starts off as your typical evil warlord, but when he starts kidnapping Celestrians to drain them dry...
The chest-opening sound after a battle meaning an item dropped, especially if it's a grotto boss.
Nightmare Fuel: Princess Simona's psychotic breakdown at the climax of the Yore arc. Seeing one of the kindest, sweetest characters in the game driven to such despair that she's literally seething with barely controlled rage and bitterly calls her own father, her people, and herself cold blooded mass murderers (which is actually kinda true) all while clearly on the verge of tears is... unpleasant, to say the least. Her sycophantic reverence towards Yore did not help matters. Thank Celestria she was brought back to her senses after Yore's death.
The Scrappy: Ivor. He talks big but doesn't ever do a good job with his Inn, at least on his own. This may have been intentional, as he's The Scrappy to all of the other villagers (except his sister, who admires him.)
Sidetracked by the Gold Saucer: While IX doesn't have a Casino, it's very easy to get distracted by playing with the Alchemy Pot, rooting out sidequests, spelunking in the grottoes or simply exploring the world once you've got a boat.
Strawman Has a Point: On the main page, the Celestrians are called out for being Smug Supers and holding the mortals in disdain, but think about it — the Celestrians have spent their entire existence practically slaving away for the mortals, protecting them from monsters and solving problems for them (like finding lost items and cleaning out their damned stables), and for what? For what amounts to largely abstract gratitude to the local guardian figure — the only actual personal gratitude the Celestrians get comes from ghosts (and let's ignore the Flat Earth Atheists like Ivor). They've been cleaning up mortal messes for thousand of years with no real end in sight — they're pretty well-justified in not thinking very well of humanity. Frankly it's a wonder that they don't hate mortalkind outright.
Fridge Horror, because you realize that eventually...they're GONNA find out what happened to Marion.
Or worse: They don't. They all go to their own graves wondering what happened to her, why she left them, and if she's happy.
The tearjerking starts off waaay before that with the Wight Knight. Turned into a skeleton and sealed away by a Yandere witch's curse, he escapes only to find that his kingdom, and his bride-to-be, are long gone. Thankfully, they'll turn into tears of happiness when Princess Simona is able to send him off to be with his beloved again.
That One Attack: The final boss's Magic Burst, used when he's low on health. The attack unloads all his MP into a single attack that hits your entire party... oh, and he can remove all your buffs before casting it, then restore his MP to max right after. Have fun if you're under-leveled.
You can actually learn this move yourself, and even spam it. As long as you have enough Elfin Elixirs to do so.
There's also Hatchet Man, which is essentially a critical hit at double power. Luckily, it has a high miss chance.
The difficulty of a grotto boss essentially hinges on whether or not it knows Disruptive Wave. As Contractual Boss Immunity means stat-lowering spells don't work on them, the only way to cause some real damage and survive is to buff yourself (Fource, Channel Anger, Tension, Kabuff...), which Disruptive Wave completely nullifies. Sages can learn it, but it will (at best) remove 20 tension from a boss.
The Dreadmaster exploits Tension boosting and multiple attacks, meaning that the main character is just about stuck until he learns Back Atcha to reflect attacks.
Goresby-Purrvis is also criminally obnoxious, given that he can attack twice and has his turn-skipping upward slice to keep you from retaliating.
That One Sidequest/Waggle: Tag Mode. It's easy enough to find all the players you need in Japan since everyone and their mother plays Dragon Quest, but players in other regions will find it much more difficult to find the required 30 different people to max out their Inn upgrades in addition to getting the additional items and treasure maps.
Two sidequests involve killing metal slime variants in what amounts to "as slowly as possible", where said targets really love running at the exact worst time: The first, which grants the armamentalist vocation, can be made much easier by using Metal Slash with the Falcon Blade (which hits twice). The second, which grants the ultimate hammer technique... can't.
Really, a good deal of the level 40 quests, all of the ultimate weapon skill quests (save shield, bow, and sword, if you know where to look in Marco's travel journals, found in the library), and anything involving Critical Hits. These range from tedious (080 'Atchet Job), to difficult (072 Jump for Joy; 074 Mr. Whippy's Wish), to sadistic (091 Critical Appraisal). Special mention goes to 090 "One Latht Tetht" for being outright ludicrous: you have to defeat 50 monsters inside the tenth floor of a grotto or deeper, all while naked.
The gladiators' level 40 quest, '105 - Challengus Maximus', can be very, very annoying and needlessly tedious. Standing around staring at a green dragon's mug until it finally decides to spew poisonous breath instead of whipping you with its tail is bad enough, but waiting for it to do that AND successfully poison your gladiator(s) can be extremely frustrating. As if once isn't enough, you have to go through this thrice; and no, coming into battle already envenomated doesn't count. In the end, the so-called challenge becomes less about your gladiator fighting a dragon while handicapped, and more about him or her actually getting poisoned by the dragon in the first place.
'A Simple Task' is not as simple as the little girl who gives it to you seems to think, Guide Dang It...
To clarify, you have to be wearing a specific combination of clothes — hat, shield, torso, feet, gloves, weapon, and accessory — without telling you what the combo is. If you've played through to this point, you will have encountered at least 75 of each of those items. No, there are no hints. Same with another fashion-related quest (thankfully most others tell you what to wear).
Finding people to tag was a lot easier if you're the type to go to conventions. It was especially easy during the time Nintendo was actively promoting the game by giving out maps.
Woolseyism: Plenty. Puns and Added Alliterative Appeal aside (which the game uses constantly to mixed results), the translation is top notch, with the fewaccents around being fairly low key and — most importantly — easily readable.
One specific outright edit, however, was the modification of the "Mr. Popo" style face option, which is a lucky thing as it was essentially blackface. It now just resembles a Slime's face.