Rock Wraiths

Rock Wraiths are dwarven legend.  They are created when a dwarf is overcame with greed, digging deeper into the stone with no respect for the rock.  The stone will rise of its own accord to strike down the greedy dwarf... but a stone once awoken does not sleep so easily, and stalks the empty tunnels, looking for more dwarves to kill, too angry to slumber once more.