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.
YMMV: Realm of the Mad God
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.
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.