Scrusters are rare Metal slugs, and the bane of MechBeast engineers everywhere. These slugs have a high iron diet, and they usually get the iron by using their ability to rust ferrous metals with their touch, and then eat the rusted metal. This is very frustrating for cave trolls, or anyone who owns a mechbeast. Gold is the porterhouse steak to the "little rustmonkeys", as cave trolls call them.
They look like Armashelts in their protoform, but are grey in color, and have rust-orange shells.