BlueBlackRed
Explorer
But a magic sword won't rust. It can lie in the crypt of an ancient king for centuries, and when your paladin picks it up it's still got a keen edge and, under the dust, a surface unmarred by rust. If it doesn't rust, then why would a rust monster be a particular threat to it?
I'll explain that science to you once you explain the physics of how spells work, how beholder eye rays work, dragons breathe fire, and so on.