Ore Louse
CREATURE 5Ore lice are six-legged insectile creatures that roost either just beneath or above the water's surface. They're highly territorial toward both strangers and each other, able to detect an intruder through the ripples in the water. Due to their diet, ore lice have incredibly tough chitin that's infused with metal. Cannibalism between ore lice is common when they're unable to locate other prey.
Though there are far more suitable environments for ore lice bordering the Plane of Air, the creatures are often found where the Plane of Earth meets the Plane of Water. This was a mystery that puzzled many—until the Plane of Metal returned between the Planes of Earth and Water. Planar researchers realized that ore lice must have hunted here before the planar schism. On the Plane of Metal, ore lice often appear in horror stories chasing down metal elementals and ferociously devouring them. Their connection to Ferrumnestra adds to their infamy.
An ore louse can smell metal as a precise sense.
An ore louse gains 5 temporary Hit Points each time its mandibles Strike either damages or breaks a metal item using its rust ability, or if it hits a creature that has the metal trait or is made of metal.
An ore louse's Strikes causes metal to rapidly rust and corrode. If it succeeds at a mandibles or oxidizing spit Strike, the ore louse deals 3d6 damage (or double damage on a critical hit) to a metal item the target is wearing or holding, ignoring its Hardness. If the ore louse hits an unattended metal item, the item takes this damage automatically. If a creature uses the Shield Block reaction with a metal shield against the attacks, the shield is automatically broken, but no other item is rusted on that attack.
The ore louse can stand and move on the surface of water or other liquids without falling through. The ore louse can go underwater if it wishes, but it must Swim to do so.