Xills visit the Material Plane, where they're often known as ethereal stalkers, primarily to maraud and to kidnap creatures back to their native Ethereal Plane. These four-armed, warmongering monsters paralyze their victims before implanting them with eggs using an ovipositor normally kept retracted behind their mandibles. Their single-minded drive to expand and conquer is so all-encompassing that while they work together dutifully and without dissent, there is little else in their lives.