When a lesser fiend has proven itself worthy of greater power and responsibility, it undergoes a mystical process that transforms it into a marilith (MĀR-ə-líþ). Mariliths are the colonels of the daedric army. They are brilliant tacticians and can wield unholy power far greater than that of any lesser daedra. Mariliths rarely enter the mortal realm directly, but when they do it is a terrifying sight to behold.
A marilith's upper body is human in appearance but has six arms, and its lower body is that of an enormous serpent. Balrogs, wraiths, incubi, succubae, and dread nymphs can all become mariliths, but any candidate chosen must show exceptional capabilities in all respects. Lesser daedra cannot, however, undergo the transformation on the material plane, unless they are at a site of intense magical power and at least one daedra noble or daedra lord is present to perform the ritual.