Demonic Spiders: The bats in the Manor of the Immortals; they inflict the incredibly annoying Confused status, making it highly likely you'll stumble right into Nosferatu.
Fanon: Pretty much all of the game's lore is this.
Game Breaker: The Spider Den dungeon formerly made it too easy to level up, allowing a player to increase from level 1 to level 10.
The best healing spell also used to fully heal everyone on the entire map. One priest could cast it two or three consecutive times without mana potions.
Pets, or at least high-level Heal/Magic Heal pets. Levelling the Heal ability to level 100 (The highest possible) results in the pet healing you for 90 HP... every 'second'. This means that many situations that would previously have been lethal are now cakewalks due to enemies simply being unable to kill you faster than your pets can heal them. Magic Heal is similar, if slightly less effective, healing you for only 45 MP per second, but this is still enough to let every single character spam their ability to no end.
As a direct result of pets, sword classes (Particularly the Warrior and Knight) have become this. Their dangerously low range in exchange for incredible offensive ability previously made them a high-risk high-reward class, with their high defense only allowing them to spend a short time within effective sword range. With pets healing them and refilling their magic, this changed; Knights can now permanantly lock enemies in the Stunned status rendering them unable to fight back the second they close to melee range, made easier by the constant healing, and Warriors can permanantly buff themselves with the Armoured status by using the untiered Helm of the Juggernaut, skyrocketing their Defense to levels that, augmented by the high Heal power of pets, they can simply ignore every single shot that comes their way, even the 200+ damage ones.
Heroic Lineage: A couple of achievements imply that every new character is the child of the former character, or at least otherwise related, and thus that 'Fame' is the leveragable prestige of the family name.
The Scrappy: Kabam!. They weren't too badly disliked after first acquiring the game from Wildshadow Studios, mostly because the game would likely have been shut down without that. Since then, aside from a few good moves such as the Haunted Cemetary and Davy Jones's Locker they have done very little to actually support the game; the Epic Dungeons are simply much harder versions of the three easiest dungeons in the game, The Shatters was designed by one of the forum-goers, the Lair of Draconis and the Ice Cave both took forever tocome out, they frequently break promises made to the playerbase, do very little to fix glitches or shut down hacking, have very poor support (often not even reading the tickets they get sent), and made a number of Pay-to-Win measures.
Most recently, they left the game completely untouched for six months. An MMO with no updates, little word from the devs, rife with hacking and cheating, a seasonal-themed Nexus that rapidly became outdated, and no word on if the game would continue to be worked on. Eventually, one of the G Ms announced that the entire dev team had been pulled away from the very active MMO to work on mobile games and "would be working on the game in the future." Two months after that and the only activity is from that same GM, who is using recycled events to attempt to breathe some life into the rapidly-ailing game. Needless to say, this has not endeared Kabam! to the game's fans.