As immortality was sacrificed to bring balance to the world, the Dargean figured a way to transfer their life energy to one another, sacrificing themselves to enable the few remaining to guard the gates for centuries to come.
However, the purity of the race had also been sacrificed and a faction of Dargean broke off from the empire. They did not want to sacrifice their lives for this cause and felt that since the magic of the world had faded, so had the glory days of the race.
With this change of attitude they sought to destroy element stones in defiance to the Gatekeepers. This however changed them forever, as forces of the outer planes vacuumed back into the world, it corrupted those that had tampered with the complexity of the ritual. They slowly became dark shadows of their former selves, tainted by the lower planes, and their metallic bodies rusted with corruption.