In the comments on my Rust Monsters: Not For the Wuss of Heart post, several people claimed that they disliked Rust Monsters because they didn’t represent any real challenge: once you knew the trick of dealing with them, it was just a tedious process of beating them to death with non-metal weapons. I think that betrays a lack of imagination on where and when they might meet Rust Monsters, but for them I have created:
Dire Rust Monster
Armor Class: 2
Hit Dice: 5*
Move: 120′ (40′)
Attacks: 2 Claws/1 Club Tail/1 pair antenna
No. Appearing: 1-4 (1-4)
Save As: Fighter: 3
Treasure Type: Nil
XP Value: 400
Looking more like an ankylosaur with antenna than an armadillo, the Dire Rust Monster share with its lesser cousin a voracious appetite for metal.
The special antenna attack is the same as a Rust Monster: non-magical metal armor or weapons crumble to dust; magical metal armor or weapons lose a plus (10% per plus chance of resisting the effect), once it loses all its pluses the next hit crumbles it. A successful hit on the monster with any type of weapon means the body was hit, and there is no ill-effect on the weapon.
Now it’s just as challenging as an Owl Bear (since it’s statted like an Owl Bear, except for its AC, a lower Morale and a different special ability, and a whopping XP bonus) and those who were bored by the original Rust Monster should be all eager to go up against it, right?