5e's Rust Monster

There's been a bit of whining in the D&D community that the Rust Monster just isn't scary enough any more. Here's a rundown of the differences:

• 2nd Edition: Rust monster immediately corrodes things it touches, eats them. Magic things have a 10%-30% chance of not getting corroded.
• 3rd Edition: Rust monster makes a +3 touch attack, corrodes things it touches, and eats them. It's a DC17 dex save to protect a magic item.
• 4th Edition: Rust Monster has to hit first (or be hit) to trigger rusting, then can hit again with a bigger attack to destroy a rusting item. This is only a once-per-encounter attack for the lower-level specimens, and a recharging ability for the higher-level ones. Rusting is a cumulative, temporary penalty.
• 5th Edition: Each time a Rust Monster touches or is touched by an item, it takes a cumulative, permanent penalty until it rusts away. Magic items are immune. 

Clearly, the worst of them all is the 2e Rust Monster, due to the generally lower scaling and scarcity of magic items. The 3rd edition version seems bad, but when you take into account Magic Mart and how rapidly the party's AC gets nearly out of reach, it's not too awful.

The Rust Monster is another iconic D&D monster, but this is in part because it's too awful. It's essentially a monster that your front-line fighters out entirely, unless you gave them time to change into leather gear, or room to escape and change. Basically, parties will do whatever they can to avoid them, which makes them not a very good monster to actually use.

In 5e, the scarcity of magic items is why they aren't affected. If you are running a campaign where you allow players to have easy access to magic items, I would strongly recommend modifying this trait. If you are playing 5e RAW, remember, your players might go a long time without ever seeing more than a few pieces of uncommon gear.

The cumulative damage bonus means players are more likely to fight them, and you can use them in groups without it being an overwhelming ruination of player gear. Players *might* decide to run and change, or they may just tough it out, drawing a backup weapon and using it until it dissolves. It's also a good time to use the Magic Weapon spell.

So it's true. The 5e Rust Monster is not as big a threat as in older editions. But in my experience running the game, that makes them a more usable enemy. They're still something that plate-wearing fighters will want to keep a healthy distance from.