Broken Base: The Paladin vs. Necromancer War caused massive debates on whether the consequences were fair.
Complacent Gaming Syndrome: As in-game wars are considered Timed Missions, players considered "warmongers" try to rack up the most kills in the least amount of time. This means maximizing damage per turn, minimizing the number of turns taken per battle, preventing pets from taking their turn, running away from monsters with high Endurance, and using equipment with short animations. This led to the build called the PoeMage, where a player uses "nuke" spells (usually requiring Cast from Hit Points or being locked in a defensively-poor armor) while a Poelala pet and guest boost their damage.
Armors with the "Fully Offensive" lean deal 25% more damage at cost of taking 25% more damage back, and "0 proc" weapons generally have inherently higher damage to compensate for the lack of special attacks (procs). These two types of equipment are combined to maximize overall damage per turn. This setup is popular for two reasons: 1. it is much easier to collect equipment with these attributes than those with more defensive abilities, and 2. this type of equipment makes it easy to outdamage monsters. This setup is so popular that at one point, the character build guide on the official forums listed nothing but high-end "0 proc" weapons and Fully Offensive-lean armors and listed everything else as an afterthought.
Pendant of the Galin is a miscellaneous item that randomly decreases elemental damage received, alongside boosting to Bonus to Hit, Endurance, and Charisma. While it's not the best misc. item for every situation, it provides a nice mix of offense and durability, which turns it into one of the most used misc. items in the game.
Gogg, the most well-known example of this game's Glass Cannon, as it hits like a truck but dies really quickly. There are many deadlier variant, such as Armegoggon. Then Shadow Gogg came with his random chance to inflict Celerity (allowing it to act for another turn). Be thankful that Shadow Gogg only hits with Light and Dark, unlike the regular Gogg, which will use Ice-, Water-, and Energy-element attacks.
Elemental Shifters, especially Windshifter and Fireshifter. For short, these guys are basically monsters that attack with two opposite elements (use one for normal attack, another for their SP attack, with are stated in their names). Darkshifter is a normal Jack-of-All-Stats, Energyshifter's attacks can drain MP, Windshifter is a tank with really high Melee/Ranged/Magic defense, and Fireshifter is a deadly Glass Cannon. Fighting them is easier now thanks to glowing-SP-bar-when-ready-to-use-skill update, but this only works when facing one enemy. When fighting groups of Shifters, one will throw its SP attack while the other one use its normal attack, and their combined SP regenerates twice as fast!
Sneaks (A type of snake) are probably the most common, but they're getting edged out of their position as "King of all monsters that make players tear their hair out." The most obnoxious thing about them is that they're very, very difficult to hit with anything except a ranged attack unless the player's character has high dexterity. However, some more-recently-introduced monsters are just as hard to hit or worse, and they don't have the ranged weapon weakness. And since status effects were introduced fairly late, monsters that use them are really, really obnoxious. And then, we have the Ancient Sneak from "Play the Harpie" quest...
Mighty Shadow Hydra have the ability to stack bleeding status effect which inflicts harm based damage whenever it hits the player with its attack, and all of its resistances are lower than 100%. Bring it down to half health, and it summons its second head, increasing its damage output and bleeding, to the point that it can deal somewhere around 500 damage per turn. Put simply, the player needs to handle it quickly before its damage output snowballed out of control.
Enjoy the Story, Skip the Game: It's commonly accepted that while the gameplay of the game can be considered unexceptional, the lore can stand on its own quite well.
Game-Breaker: Essence Orb misc allows you to trade HP for SP. SP were originally a limited resource that can be used for various purposes, such as misc upkeep, and armor skills that recharges overtime making them harder to spam to your heart content. Essence Orb broke that notion, by allowing you to have as many SP poll as your HP allows. This particularly had a ridiculous implication with quick-cast SP skills since its entirely possible to reattempt their casting so long as you have enough HP to spare.
Purple Rain can be used once per battle, cast it to record the current HP, MP, and SP total on both side, and a second casting will use SP to attempt returning to the recorded state. The catch is, while Purple Rain records HP, MP, and SP it doesn't record current status effects. The way this is primarilly abused is by casting skills that generate free turns such as subrace armor, Shadowfeeder Pendant, or love potion prior to the second cast of Purple Rain, essentially making them free, followed by nuking down the enemies with armor skills. This become much more abusable as the options for Quick cast status effects got wider.
The revamped Subrace Armor is considered this, thanks to being a level appropriate armor with a bunch of passive and active bonus on top of it. For Guardian, Werewolf, Vampire, and Werepyre subrace armor in particular is packed with a quick-cast skill for Fear, Control, and Panic respectively, offensive stats boost, and a transformation that significantly improve damage dealt for an SP or MP upkeep cost. To top it off, every subrace contains 4 variations that compress 2 elements at once making them usable in almost every situation, with the caveat of one of them costing Z-Tokens.
Shadowfeeder Pendant can be clicked to give Celerity, giving another turn. Being a guaranteed free turn generator, Shadowfeeder Pendant can be abused in various ways, making it a ridiculously useful misc item.
Good Bad Bugs: During the "Divide by Zero" war, the monster pool was abnormally strong, leading to waves of monsters that were 30 levels above the character's level. This also meant farming was made easier, but slowed war progress.
The Power Katana weapon caused some odd bugs. In AdventureQuest, the armor the player character wears determines the number of hits done with each attack during a turn, but it also determines what percent of the weapon's damage is done per hit. The Power Katana, probably due to it being the only item that scaled with your level at that time, did not play nice with the latter. Instead of damage being divided over each hit, each hit did full damage, which was insanely broken if the player paired it with an armor that performed several weak hits, allowing you to do up to six or seven times standard damage. The bug was, however, eventually patched.
Weekly releases tend to have a few hiccups before a patch later in the day, such as the 2015 Giftbox armor bugged to deal 100% damage for two hits rather than 50% damage each. Banshee Form armor had a bug that lied unnoticed for months. Banshee Form, on paper, was a strictly inferior Darkness-element armor compared to others, but in implementation, it was bugged to deal double damage compared to other armors of the level. People who actually used Banshee Form would have a much easier time clearing the game before it was patched.
Junk Rare: Due to game engine updates and that many old items are only suitable for a range of levels, many old rare items become this.
Sequel Displacement: Due to the original game being unrefined at best, other Artix Entertainment games have eclipsed the original AdventureQuest in popularity. However, many of the characters prevalent in the other games stem from the original game.
The "Unbeatable" and Void monsters are mostly designed as these.
Shadow Storm. The way it works is, it starts the battle with a powerful two-hit SP attack that randomly hit with light or darkness element, and it spends the next four turns to recharge its SP and HP until it can use its SP attack. Rinse, and repeat. Its SP attack also has an effect to reduce the player character's damage output, and you have 25% chance to get stunned and do nothing. It actually has quite a low starting HP, but it has a much higher maximum HP, which means it can regenerate itself until it has three times its starting HP if your offensive power is unable to compete with its massive HP regeneration.
And he was even worse in its original version because of a programming mistake which caused its damage output to be doubled, enough to outright one shot a fragile character if they are caught in the wrong armor set up. This bug has been fixed, and the Shadow Storm has been re-adjusted since the damage fix.
Ryn the Undying is one for most players due to his complex system of attacks. His default attack is randomly chosen between Fire and Dark elements, making resistance against both hard. He also uses special attacks depending on if he has MP and SP and if he had inflicted a Standard Status Effect on the player character, so the player needs to watch every piece of information on the screen to make sure what attack he'll use next. Then there's the fact his special attack has a chance of downright killing any player character that isn't a pure human, but the game never tells the player why he can OHKO the player character. Unlike most other bosses of this difficulty, defeating him is required to unlock more Celestial Haven quests. Overall, he's Guide Dang It! in boss form.
The boss of third Frostval 2015 quest, Ancient Fruitcake Zard. It can paralyze the player's character over and over again with its bite attack. The only way to avoid paralysis is to lower the character's water resistance enough, or to otherwise let pets and guests deal enough damage.
Falerin's ramblings in other contexts will go over people's heads without a bit of esoteric knowledge. For instance, he mentions whether it is proper to use 'antediluvian' as a synonym for 'old' if Lore didn't have The Great Flood; the word 'antediluvian' literally refers to 'before the flood'.
"The Sweep", an ongoing rebalance operation which is supposed to be applied to older items as well as new ones. Whilst all new items are at the new standards, most older equipment has yet to be fixed. However, as standards end up changing at infrequent intervals, even 'swept' equipment can become outdated.
Everything that Lord Barrius was working on after he was fired falls in here now, as almost all of it is going to have to be reworked and putting it off even longer (the Paladin and Necromancer Class sweeps, the Knight Class storyline) or just neglecting it outright (virtually any Shadow-related storyline or ones that directly involved any of LB's Character).
Word of God: Mostly, Falerin. (In this case, literally. Falerin, the head writer, is also the NPC Caelestian God of Evil.) With Lord Barrius and Eukara coming a close second. Of course, none of the other writers (and the team)'s comments are considered any less informative/important despite this.