Diving into my old and new Dark Sun books (as well as replaying Baldur’s Gate) gives me an interesting idea, a weapon property that characters can obtain (BUT DON’T WANT!)
Feeble: “The quality of you weapon has seriously degraded overtime. Perhaps the materials that crafted for your weapon were either meant to be temporary or not intended for constant stress. While wielding this weapon, targets have resistance to its damage. Targets that have resistance to non-magical weapons are immune to attacks from this weapon. Furthermore, rolling a Natural 1 on the die destroys this weapon. In addition, armor with the feeble property grants -1 AC penalty upon any armor above leather. If a target scores a natural 20 against your armor, it shatters. However, if either the target or attacker is wielding a feeble weapon and the other has feeble armor, this quality is ignored. However, the Nat 1/Nat 20 rule still applies.”
Now, this is pretty damn harsh! How would it be applicable? Perhaps a recreation of the Iron Crisis/Bhaalspawn saga would work for this? Maybe the majority of weapons in Athas would carry this trait (considering they’re mostly made of rock and bone, something I can’t imagine taking too much abuse before breaking.)
On top of that, I’d probably replace the Rust Monster’s ability with the ability to make weapons feeble. Furthermore, if it attacks a feeble weapon, it is automatically destroyed. 5E Rust Monsters are a lot more intimidating than their 4E counterparts, but they’re still not scary. To be fair, the Tarrasque needs some fun buffs as well.