The current edition of Dungeons & Dragons severely nerfed one of the most terrifying monsters in the series. D&D's Rust Monster is an insect-like creature with two massive antennae, and few things inspired as much fear in old-school adventuring parties as the sight of one of these beasts.
There are many monsters D&D parties should be scared to face. Dragons are always a threat, while Beholders have the ability to annihilate players where they stand with eye beams. Mind Flayers are also terrifying, as their Mind Blast ability allows them to incapacitate an entire party in one action. Evil adventuring parties are also a huge threat, since they act as a mirror to the players' own abilities, but these kinds of enemies are usually loaded with great magic items to loot, so players might not mind fighting them as much as monsters.
The enemies above are usually reserved for mid- to high-level parties. But in early D&D, there was one low-level monster that remained a threat to the party at all times, as it had the ability to rob players of their precious magic items.
D&D's Powerful Rust Monster Could Eat Players' Best Loot
The Rust Monster was so terrifying because it could destroy magic items. The antennae of a Rust Monster would instantly annihilate any metal they came into contact with. This fact alone might scare martial warriors, as their weapons and armor could be melted away from their bodies. In Advanced Dungeons & Dragons (the second edition of D&D), however, Rust Monsters could also destroy any metallic magic item. A magic item had a percentage chance equal to its plus-value to evade the effect, with +1 having a 10% chance to be safe, a +2 having 20%, and so on. This meant a +5 weapon was a coin flip away from being utterly destroyed. In third edition, the magic item had to pass a steep DC 17 Reflex save in order to be saved. This meant there were many years when a room full of Rust Monsters was one of the scariest traps a Fighter could fall into.
Rust Monsters still exist in the current edition of D&D, but they're nowhere near as scary as before, as they can no longer affect magic items at all. Their effect can still cause major annoyances, especially if a character has spent a lot of gold on a strong suit of armor, but that's easily replaceable. The new version of the Rust Monster is more of a nuisance than a threat, and it no longer inspires fear in the hearts of Dungeons & Dragons hoping to avoid losing their characters' most prized possessions.