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.
Breather Boss: Gimle in The Millennium Girl. It's insanely bulky, but it isn't a threat at all when you consider that you just got past the Iwaoropenelep. Doubly so if you have Peace Ballad, as it removes any need for even TP restoring items.
Crowning Moment Of Awesome: F.O.E.'s are not entirely immune to the instant-kill aspect of Head Pierce. Taking one down in one shot is very satisfying.
Crowning Moment of Heartwarming: The video that plays when the Story Mode group in The Millennium Girl reaches the 5th strata. Frederica begins to feel very depressed at the sight when the Highlander simply takes her hand.
Demonic Spiders: Petaloids their variants in Etrian Odyssey loved nothing more than to chain-sleep your entire party, thus allowing the other enemies to unleash a world of hurt on you.
They appear in Legends of the Titan as well, although thankfully they'll only target one party member... unless you damage them.
The Bloodant FOEs in Etrian Odyssey. The first time you encounter them on B12F, they don't hit very hard, but have a lot of HP. Plus, they have infinite regeneration and the ability to summon both Bloodants and Deathants. To top it off, with the battle against the Royalant, they'll continually spawn in a corner of the room and rush towards the battle. Enjoy a main dish of Royalant, a side order of Bloodants with a generous helping of Deathants with your-ass-getting-kicked sauce. Thankfully, they are much easier in the remake.
In general, there is at least one type of enemy on each stratum in every game that could qualify as one. In particular, the final strata have plenty of enemies that can get very dangerous unless handled right. The Drowned City has the Longicorn Beta on the final floor that can summon multiple enemies at any time, and then throws them for high damage to the entire party. It's also highly durable, which makes it difficult to shut it down with statuses long enough or kill fast enough to stop it from throwing enemies.
In The Drowned City, there are also monsters that are otherwise weak, but they qualify as Demonic Spiders because if you don't kill them fast enough, they will summon or transform to FOE-type monsters. A really nasty surprise if you don't expect it.
And in Legends of the Titan, the Hollows are meant to be a crash course in utilizing Bindings, and it shows. Even the weakest Hollow type has evasion that's through the roof, so unless you have a Sniper or Arcanist in your party, just hitting one can be a Luck-Based Mission!
Also from Legends of the Titan, there are enemies in the final dungeon that can petrify your entire party with one move. While they only target one member of your party until they take damage, they're occasionally paired with an enemy (a Hollow, no less) that can deal that one point of damage to get a power boost.
Designated Villain: Visil in Etrian Odyssey, who as it turns out is trying to save the world.
Arthur from Millennium Girl receives a lot of attention from fans due to being rather comical.
Esoteric Happy Ending: The first game. Hooray! You've defeated Visil and uncovered the truth! Too bad it involved killing the guy who probably saved the world and likely plunging Etria into an economic disaster. This gets fixed in the remake.
Fanon: Literally encouraged by the developers! As explained on the first game's website (Director's Diary, entry 5), one of the major elements the games take from "old-school" dungeon crawlers is that the party is meant to be defined largely in the imagination of the player. How they react in detail to what's going on, what they adventure like, how they interact with one another, is meant to be up to the player to define. This is why the games only ever describe your actions in the broadest of terms - they want to encourage you to invent your own interpretation and "canon" for what your characters do and say. This is why Untold's Story Mode is more divisive than the other titles, as having five defined characters as opposed to the party that lives in the mind of the player really goes against the wider spirit of the franchise.
Game Breaker: In a game where most classes had roughly 300 HP at max level, Etrian Odyssey's "Immunize" was the difference between most enemies hitting for 250 and for 25. Because Atlus has a personal vendetta against anyone who ever succeeds in any of their games, rather than rebalancing it, they just removed Immunize entirely from Heroes of Lagaard. Oh, and no more Healing and Relaxing for Troubadours, either. Have fun!
Which didn't help much, because they also took the opportunity to boost some unused skills, and did a bit too much. In Heroes of Lagaard, the Hexer skill Revenge was boosted to deal 255% of the damage the Hexer had taken for only 19 TP once mastered, which means a Hexer with items to boost max HP, 1 HP left, and enough AGI to move first can be devastating.
To elaborate: Revenge deals set damage depending on how much HP a Hexer has lost, ignoring enemy's defense, resistance, immunity, etc.; if a hexer can deal 1000 damage to a mook, they can deal that much damage to a Boss. In Heroes of Lagaard, not only was Revenge's strength buffed, the HP of FOEs and bosses were nerfed. In said game, the highest HP among non-Final Boss or Bonus Boss is around 3000-4000, but said bosses have a massive amount of defense. With proper equipments and setup, Lagaard's Hexers can dish out between 1500 to 2000 damage per Revenge. A Boss Fight using other classes can last 10 turns or even longer, while Hexers can happily wipe out a boss in possibly two hits.
While not as broken, a Hexer with Evil Eye and Suicide can command the enemy to attack itself instead of the party, allowing the player to attack an enemy without worry of being hit. There's also Betrayal, which forces all terrified enemies to attack each other. Adding in Relapse, it's possible to cripple an enemy for the rest of the battle.
In The Millennium Girl, Evil Eye was buffed. Instead of just targeting one enemy at a time, it targets a row of them. Curses increasing ailment chance make it more reliable as well, so Hexers become even more powerful than they were before.
The Whip It Good Dark Hunter's Climax in the same game, once mastered, kills any enemy vulnerable to instant death with less than 55% of its HP (previously, it only had a 20% chance of working, even when mastered). Most bosses are immune to Climax, but FOE's aren't; having Climax mastered essentially halves the duration of any FOE encounter.
Their Dominate Limit Break is guaranteed to go last, but will bind any enemy, including bosses, preventing them from using their skills (though some exceptions exist). That enemy can waste a turn trying to use a skill that requires the bound limb. Couple that with Dark Hunter's Ecstasy, which deals massive damage to a completely bound enemy, and you can often win quite easily. Also, using a Survivalist's 1st Turn skill allows the Dark Hunter to use Dominate before anyone else moves.
A War Magus' Cursecut can drain TP from an enemy that's been cursed (best done with a Hexer, which, as mentioned above, is a Game Breaker in and of itself). War Magi can also transfer their TP to other characters by the use of their Transfer skill. With this combo, you have potentially limitless TP. A shame that this is pretty much all that a War Magus is good for...
In addition, the Hexer's Torpor immensely aids the War Magus' Sleep Cut, allowing the party to deal pretty massive damage while the enemies are asleep.
Heroes of High Lagaard's Force skills in general are fairly severe Game Breakers. The Gunner's guarantees that you'll stun an enemy for that turn and the Protector's negates all damage and status effects for one turn, for example. At the end of the game, it's possible to use them every turn by dedicating two characters to feeding the Force skill users Axcelas. However, not only do they cost a lot, but also require plenty of materials in order to buy them.
The Dancer's bottommost dancing skills in Legends of the Titan. These passive skills give an increased dodge chance, the ability to hit multiple times in a single attack, and the chance to stun an enemy upon connecting with a normal attack. It only takes three skill points to unlock the second skill, compared to the sixteen (at least eight of which are dumped in a useless skill regardless of what weapon you use) it took to unlock its predecessor Swashbuckling in The Drowned City. Dancers are also able to use a different skill to make allies in the same line follow up on their attacks, meaning it's possible to have your entire front line attack multiple times per turn.
Want to crank the fun Up to Eleven? Give them the Nightseeker subclass and make them Dual Wield. The multiple attacking can trigger both weapons individually. If you have Sword Dance maxed, your Dancer can potentially attack eight times per turn. By the way, did we mentioned that the Dancer is both a buffer and healer?
The secret class Imperials in Legends of the Titan count as well. They're restricted to using only one type of weapon (they can't equip a subweapon alongside their class-specific weapon) but are capable of dealing thousands of damage without attack buffs. To balance the class, they're given a few cooldown turns until they're allowed to use it again. However, they can use two skills to cool down their weapon (which deals damage as well) and then use an attack that charges up their next turn's attack power (which more than doubles their power even without the skill maxed), which happens to be the same turn they're allowed to use the powerful skills again. If an enemy somehow manages to survive a few of those attacks, there's even a skill that removes the cooldown time for three turns and immediately cools down their weapon after a certain amount of overheats occur in a battle, allowing the character to deal massive damage without any drawback for three turns.
Once a Nightseeker in Legends of the Titan hits high enough level to be able to use Venom Throw, maxing it out allows them to inflict a poison status that does a fixed 700 damage every turn for several turns, enough to make a large dent in even most bosses' HP. Combine this with Spread Throw and Auto-Spread which allows them to hit every enemy with the next 2 throw skills and a chance to use said skill for free at the beginning of the battle, and they can take out most random encounters in a single turn with very little TP used. If you then give them Arcanist as a subclass, you can not only use one of their passive abilities to increase the chance of landing the poison status on even strongest enemies, but also gain back any TP you spend to use the move if the poison sticks on at least a single enemy thanks to their TP Return.
Hexers break the game again in The Millennium Girl with Stoning Curse, an extremely reliable petrification spell (which instantly kills the target) against normal enemies with a low TP cost. Unless there's a massive group of enemies that require Evil Eye, Stoning Curse is all a Hexer needs to use outside of F.O.E. fights and boss battles.
Again in The Millennium Girl, there's the Gunner skill Action Boost. It allows you to take any action twice (three times if you level it up enough) for your next turn, but Action Boosted skills still require TP for each use. The game breaker is, provided the skill that triggers it is increased by Boost, all attacks in that chain are boosted. This allows you to fire off multiple powerful, Boosted skills (such as Ricochet) without any drawback, as long as you have enough TP.
Good Bad Bugs: You can skip Fenrir in the first game by exploiting the fact that FOEs maintain aggro even with a wall between you to lure him into a corridor so you can run past him. While you can't go far on the 6th floor without going back and killing him (as you need to report Fenrir's death to do so), it does allow you to warp to town, save, and fight stronger monsters for better gear and get a free turn on Fenrir by attacking him from behind, as well as open some new quests. This is all very helpful, as Fenrir is an Early Bird Boss.
The Medic's Immunize skill in the same game. It was intended to reduce only elemental damage, according to the in-game description. However, the different physical attack types (Pierce, Slash, and Bash) were considered element types as well, turning it into a well-known Game Breaker. It was cut in Heroes of Lagaard, then made its reappearance The Millennium Girl after it was fixed.
In The Drowned City, while the Monk's Fist skills require you to fight unarmed, for some odd reason, the second slot counts as a Weapon. If your first Armor Slot is blank, a Monk can use his/her fist skills with a Mace, even though he/she doesn't have the Shogun's Second Sword class skill. Whoops.
In Legends of the Titan, "Auto" skills activate at the beginning of a battle, giving you a buff immediately without costing a turn. However, since the non-"Auto" variants of the buff do cost a turn, they actually last one turn less than their "Auto" variants (because it activated on the middle of your turn, and once the turn ends the buff's duration ticks down one turn). Especially useful with "Auto-Throw", which usually just lasts for one Throw skill, but when activated via Auto-Throw can be used twice. And seeing as mentioned above that Venom Throw is one massive Game Breaker on its own...
There are two notable and extremely useful glitches in The Millennium Girl; one allows infinite replication of any item that can be used in battle, while the other lets you pass down a large number of skill slots from a grimoire in synthesis without actually consuming it.
Hell Is That Noise: In Legends of the Titan and The Millennium Girl, a simple "ding!" sound plays whenever a FOE takes notice of you and starts actively chasing you down. A simple little thing, but you'll quickly learn to dread that sound, especially if you're a veteran to the series.
Moe: Present throughout the series, but the female Yggdroids from The Drowned City take the cake. The males look like you'd expect humanoid robots to look, but the females really had moe shoehorned onto them. They're tiny, have human faces and look like they would break if you looked at them too hard. Any why would robots need towear glasses?
Abigail from Heroes of Lagaard and Missy from The Drowned City also count.
Moral Event Horizon: In The Drowned City, not only does Olympia betray the party after pretending to guide them and leave them to die against seemingly impossible odds multiple times, its heavily implied that she similarly led countless other explorers to their deaths, possibly even murdering them herself, thanks to her orders to keep explorers from discovering the Deep City at any cost.
Player Punch: Early in The Drowned City, a quest becomes available to locate a camping-obsessed guild that has been missing in the labyrinth for several days. Following the clues they leave from campsite to campsite, the last you stumble on is described as a scene of carnage (blood everywhere, tattered and broken equipment and whatnot); naturally, you believe they were all killed by monsters. Subverted when you go to report the quest at the pub, as Missy almost flat-out tells you that the guild members are freakin' fine, and that all the blood at the campsite was from the monsters that interrupted their beauty sleep.
Played jarringly straight later: If you agreed to help Hypatia and Agata enter the second stratum, then you eventually find them there, and Agata presses you to tell him the location of a nest of Sea Wanderers you found earlier while Hypatia begs you not to, as she already had a traumatizing encounter with them before. You just decide whether to tell him or not and think nothing of it when he runs off to find them. Then you decide to follow him, and go to the room and find one of the two fucking dead while the other is cradling their body. There is no way to avoid this happening, as saying "Yes" or "No" only determines which dies (saying "Yes" means Agata dies, while "No" kills Hypatia). There is no way to back out of this, except for refusing to help them enter the second stratum in the first place. Then you literally never see them again, and you're free to pretendthey gave up and went home peacefully if you'd like. A bit anticlimactic, but hey.
Replacement Scrappy: When early info about The Drowned City was released, and fans learned the original classes wouldn't return, Gladiators were blasted as being generic and vastly inferior 'replacements' for the Dark Hunter class, despite players not knowing anything about it beyond the physical appearance of one representative. Thankfully, this reaction died down over time.
Even funnier when you finally found out that Gladiator is supposed to replace Landsknecht instead. note The Princess gets the Landsknecht's ability to equip heavy armor, while the Gladiator is a straight combatant; while their armor choices emulate Dark Hunters, they generally lack the ability to dole out status effects unless they invest in Stun Attack. But in turn, when compared to Landsknechts, both classes can specialize in two weapons: Sword and Axe/Hammer, and their sword skills rely on hitting as many enemies as possible, while their other weapon skill rely on hitting one enemy as hard as possible.
Scrappy Mechanic: While Grimoire Stones in The Millenium Girl offer a lot of flexibility, one big problem with them is that the skills you can obtain in one is random. Creating the ideal stone will likely take a lot of skill point manipulation and praying to the random number gods that the right skills drop quickly.
That One Attack: The Yggdrasil Core's Cell Membrane in The Millennium Girl. It prevents any and all damage for a turn and releases a painful party-wide counter in return for getting hit. If you just so happen to have a character that has the Highlander skill that may cause an attack upon being dealt damage, you may go down from a single attack triggering a chain. While it's predictable with a guide that explains the boss' patterns, it will break the pattern if you apply enough buffs, meaning you can die on any turn you choose to attack.
In the original Etrian Odyssey, the boss' original incarnation, Primevil, had a much nastier version of Necrosis that was very accurate and retained the instant-death status effect infliction, usually spelling death for the party. Even with all the strategy you put into the battle, there's a chance it'll decide to use it.
That One Boss: Iwaopeln in the original Etrian Odyssey. You need to beat every single F.O.E. on the floor to actually kill it on a floor completely filled with them. While it's possible to fight and beat Iwaopeln before nearby F.O.E.s reach you, it just instantly respawns if there's so much as a single one left. He also has a really powerful attack that will kill at least two of your party members if you don't have Immunize. Fortunately, this is not required in the remake, as they disappear as soon as the bird is defeated, although it can use the F.O.Es to assist it in battle, as well as respawning them if it sees you.
They Changed It, Now It Sucks: When the first preview screens of The Drowned City were released, some fans complained about the new seafaring setting and the new roster of character classes, bemoaning the loss of the classes from the first two games.
Viewer Gender Confusion: All classes have four character portraits to choose from. Two are male, and two are female. This is highly important information for the Survivalist, Troubadour, and Hoplite classes in particular, which have some portraits that can only be identified via process of elimination.
Woolseyism: Atlus changed the names of the character classes during translation; Landsknechts were originally Swordman, Protectors were Paladins, Survivalists were Rangers, and so on. This may have been done to give the game a more original flair and help it stand out. A later example from The Drowned City is Beast King to Wildling, probably because (like most classes) you can make a female version, and it didn't change the class name like it did for Prince/Princess.
For the rest of the classes, it was more than likely to avoid classes having the same first letter in their name as to make it easier for the item shop menu to characterize them. It would have been a little difficult to tell the difference between Princess and Phalanx or Ballista and Beast King (the class names in the Japanese version).
The Millennium Girl, with the addition of the Highlander class, had the abbreviation icon as "Hi" in the English version, breaking this pattern. If future Untold games are released, it's possible this will be implemented in similar situations.