Rust Monster

Medium monstrosity, unaligned

Armour Class: 14 (natural armour)
Hit Points: 27 (5d8 + 5)
Speed: 40 ft.

Senses: darkvision 60 ft., passive Perception 11
Languages: –
Challenge: 1/2 (100 XP)

Abilities

Iron Scent – The rust monster can pinpoint, by scent, the location of ferrous metal within 30 feet of it.

Rust Metal – Any nonmagical weapon made of metal that hits the rust monster corrodes. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed. Nonmagical ammunition made of metal that hits the rust monster is destroyed after dealing damage.

Actions

Bite – Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) piercing damage.

Antennae – The rust monster corrodes a nonmagical ferrous metal object it can see within 5 feet of it. If the object isn’t being worn or carried, the touch destroys a 1-foot cube of it. If the object is being worn or carried by a creature, the creature can make a DC 11 Dexterity saving throw to avoid the rust monster’s touch.
If the object touched is either metal armour or a metal shield being worn or carried, its takes a permanent and cumulative −1 penalty to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed. If the object touched is a held metal weapon, it rusts as described in the Rust Metal trait.